Gemara

(R. Yehudah): Chachamim who taught the Kohanim laws of Shechitah, Kabalah and Zerikah received stipends from Terumas ha'Lishkah.

(Gidal bar Binyamin): Two judges who made decrees about theft received stipends from Terumas ha'Lishkah.

Pesachim 113a - Rav (to Rav Kahana): Flay a carcass in the market for wages; do not say 'I would rather take Tzedakah, for) I am a Kohen (alternatively - the great Kahana), this is a disgrace for me!'

Avos 1:13: One who uses the crown (of Torah for personal benefit) will cease from the world.

Avos 2:2: Any Torah not accompanied by work will not endure, and in the end it will cause sin.

Avos 4:5: Anyone who benefits (financially) from Torah removes his life from the world.

Kesuvos 105a (Rav Yehudah): The judges who made decrees in Yerushalayim received stipends from Terumas ha'Lishkah, 99 Manos in all. If they were unhappy with this, they received more.

Objection: Were they Resha'im (who take more from the Tzibur than necessary)?!

Correction: Rather, if this was not enough, they received more, even if they didn't want to receive more.

Kidushin 70a - Rav Yehudah (to Rav Nachman, who was building a Ma'akah): A Parnes of the Tzibur may not do Melachah in front of three people!

Bava Basra 8a: In famine years, Rebbi opened his storehouse to Talmidim, but not to ignoramuses. R. Yonason ben Amram pushed his way in and requested food. He denied having learned even written Torah. Rebbi did not want to give to him;

R. Yonason: Please support me, just like Hash-m feeds dogs and ravens!

Rebbi gave him, and later regretted having given his food to an ignoramus. He later found out that he had given to his Talmid R. Yonason, who is loathe to benefit from his Torah. Rebbi announced that all could take food (so no one would need to benefit from Torah).

Rishonim

Rambam (Hilchos Matanos Aniyim 10:18): One should avoid taking from people if at all possible, even if he must suffer. He should not impose on the Tzibur to support him. Chachamim commanded to make Shabbos Chol rather than take Tzedakah. Even if a respected Chacham became poor, he should not take from people. One should not say 'I am a Chacham, or a Kohen - support me!' Great Chachamim chopped wood, carried beams, drew water, or were smiths rather than request from the Tzibur. They did not accept offers of money.

Rashbam (Bava Basra 110a DH v'Tol): One might have thought that it disgraces Torah if a Chacham does menial work, just like if he has a stain on his garment. Rav taught Rav Kahana that it is not a disgrace.

Rambam (ibid. 19): If one cannot survive without taking, e.g. he is old, sick or afflicted, but he is too haughty to take, he is responsible for his own death. The pain he inflicted on himself is a sin. If one needs to take but rather lives a life of hardship to avoid imposing himself on the Tzibur, before he dies he will support others from his money. About such people it says "Baruch ha'Gever Asher Yivtach ba'Shem".

Source: Yerushalmi Sof Pe'ah, brought in R. Shimshon Sof Pe'ah.

Rambam (Pirush ha'Mishnayos Avos 1:13): One who intentionally is financed through Torah and benefits from it will die. A Chacham may be served only by his Talmidim.

Rambam (ibid. 4:5 and Hilchos Talmud Torah 3:10): If one plans to learn Torah, not work and receive Tzedakah, this is Chilul Hash-m and a disgrace to Torah. He harms himself and removes his life from the world to come, for it is forbidden to benefit from Torah in this world. Chachamim taught that one should love work and despise positions of authority. Any Torah not accompanied by work will not endure; in the end he will rob people. It is a mistake to think that people or communities are obligated to support people who learn Torah all day.

Rebuttal (Kesef Mishneh): In Yerushalayim many Chachamim received stipends from Terumas ha'Lishkah, i.e. judges who made decrees, those who taught the Kohanim laws of slaughter and Kemitzah, and those who checked Seforim. This was permitted because they taught (or checked) all the time and had no income, so the Tzibur was obligated to support them (Tosfos 105a DH Gozrei, 106a DH Mevakrei). They received Shekalim that the Tzibur was forced to give. All the more so, nowadays in Galus we may force people to support Chachamim necessary for the continuation of Torah, teachers of children and judges.

Rambam (ibid.): In every generation there have been very poor and very rich people. Surely, the rich were willing to give to the poor! Rather, the poor preferred to subsist on their meager incomes. Chachamim like Hillel and R. Chanina ben Dosa were very poor. They saw that it would be Chilul Hash-m to take money from people, lest Torah be cheapened in people's eyes, i.e. Torah would look like a profession from which people finance themselves. Karna drew water, and was a judge. He would ask the litigants to get someone to draw in place of him or pay him what he will lose in the time he judges them.

Rebuttal (Kesef Mishneh): One cannot learn from Hillel! At the beginning he was one of thousands of Talmidim; perhaps support was given only to the most known Talmidim or those who could not support themselves. Surely, when he taught Yisrael he had ceased to chop wood! R. Chanina ben Dosa had no need to take from people; Shomayim would grant all his desires, just he did not want to benefit from this world. Karna would smell wine and tell the owner how long it will last (Kesuvos 105a). Surely, one who can support himself so easily may not take money!

Rambam (ibid.): R. Yonason ben Amram was insistent not to be supported due to his Torah.

Rebuttal (Kesef Mishneh): We learn the opposite from this. Rebbi wanted to support only Chachamim! R. Yonason went beyond the letter of the law, but the others accepted support due to their Torah!

Defense of Rambam (Einayim l'Mishpat ibid.): Perhaps Rebbi supported Talmidim in famine years when they could not support themselves and were considered Aniyim. When giving Tzedakah to Aniyim, Chachamim have precedence.

Rambam (ibid.): The Torah allows a Chacham to give money to people and they will give to him profit earned through it. Also, we may declare that no one may sell until the Chacham sells his merchandise, for merchants themselves often grant this to someone they want to honor even if he is not a Chacham. Chachamim are exempt from taxes and certain obligations such as building the wall around the city. The Gemara says that one who wants to benefit from others like Elisha may do so. This means to occasionally accept lodging or a meal, but not regular stipends!

Rambam (Hilchos Sanhedrin 25:4): A Parnes of the Tzibur may not do Melachah in front of three, lest he be disgraced in front of them.

Pischei Teshuvah (CM 8:5): Here, Parnes does not refer to a leader, rather to a judge over the Tzibur.

Poskim

Shulchan Aruch (OC 156:1): After learning one should go to his occupation, for any Torah not accompanied by work will not endure. In the end it will cause sin; poverty will make him transgress Hash-m's will.

Beis Yosef (DH v'Achar): One might have thought that it is better to learn Torah constantly. The Mishnah (Avos 2:2) teaches unlike this, for when his money runs out he will need to pursue income and will not even be able to fix times for Torah.

Bi'ur Halachah (DH Sofah): Most people should work. However, there are always a minority of individuals who can adopt R. Shimon bar Yochai's approach (Berachos 35b), to devote themselves totally to Torah and Hash-m will help them find income. In particular, if there are people willing to supply his needs so he can learn, he need not work, just like Yisachar, who was supported by Zevulun.

Kaf ha'Chayim (7): One who need not work must be very careful not to waste any time, and all the more so one who takes money to learn.

Shulchan Aruch (YD 255:1): One should avoid taking Tzedakah if at all possible, even if he must suffer. Chachamim commanded to make Shabbos Chol rather than take Tzedakah.

Birkei Yosef (DH v'Al): Chachamim taught that 'one should not take from people' to include even gifts. However, for the preservation of Torah it was permitted. Tana'im and Amora'im were stringent not to take; this was beyond the letter of the law.

Rema (YD 246:21): One should make his Torah primary and his work secondary; he should minimize work and engage in Torah. Each day he should work as much as needed to live, if he has nothing to eat; he should learn Torah the rest of the day and at night.

Yam Shel Shlomo (Chulin 3:9, brought in Taz 7): Tosfos (Bava Metzi'a 70b DH Tashich) says regarding the Heter to lend to Nochrim on interest 'Kedai Chayav' (for as much as he needs to live) that nowadays due to government taxes there is no limit. We can say the same to justify taking money to learn even if one has money. Even those exempt from taxes have great expenses to teach Torah to their children and to marry off daughters to Chachamim.

Rema (ibid.): It is a great attribute to support oneself - "Yegi'a Kapecha Ki Sochal Ashrecha v'Tov Lach". If a healthy person plans to learn Torah, not work and receive Tzedakah, this is Chilul Hash-m and a disgrace to Torah. One who is old or sick may be supported by others. Some permit even if he is healthy.

Source (Gra 62): The latter opinion learns from the judges in Yerushalayim (Kesuvos 105a).

Rema (ibid.): The custom is to support the Rav of the city lest he need to work in public and disgrace Torah in the eyes of the masses. This is only if the Chacham needs assistance. Some are more lenient to allow a Chacham and his Talmidim to receive support in order to engage in Torah comfortably.

Beis Yosef (DH u'Mah she'Chosav Kol): We infer from the Rambam that most big Chachamim in his generation took support; this was the way of Chachamim of old. Tashbatz (Teshuvos 142-148) rebuts all the Rambam's proofs. It is proper to take support, for without this Torah would not be learned.

Or Zaru'a (brought in Beis Yosef DH Kasuv b'Hagahos): A Tosefta forbids to support a Chacham who engages in needs of the Tzibur from Tzedakah, for that is a disgrace. People may support him from Ma'aser Oni, for it is not evident that it is Ma'aser Oni.

Rema (ibid.) Nevertheless, it is Midas Chasidus to support oneself and learn. This is a gift from Shomayim; not everyone can do so and become a Chacham.

Kesef Mishneh (Talmud Torah 3:10 DH v'Acharei): The Rambam requires one to learn a trade, but permits one to receive from people if the trade does not support him. However, from Pirush ha'Mishnayos it does not appear this way. In any case, when the Halachah is not clear, we follow the custom; Chachamim before and after the Rambam were paid by the Tzibur. Even if the Halachah is like Pirush ha'Mishnayos, "Es La'asos la'Shem Heferu Torasecha" - Torah would be forgotten if Chachamim had to support themselves.

Shach (20, citing Yam Shel Shlomo ibid.): If one who teaches Torah in public can support himself without Bitul Torah, e.g. to lend money on interest (in a permitted way), it is forbidden to be supported by the Tzibur. A Chacham may give money to the Tzibur and tell them to invest it for him to get profit. If he lacks money to support himself, it is an Aveirah to decline support, even if he knows a trade, for it will detract from his learning.

Note: Perhaps he learns from the judges in Yerushalayim. If their stipends did not suffice, they received more, even if they didn't want.

Shulchan Aruch (CM 8:4): A Parnes of the Tzibur may not do Melachah in front of three, lest he be disgraced in front of them.

Question: According to the Rambam, Chachamim may not receive from others. If a Parnes may not work, how will he support himself?

Answer #1 (Tashbatz 1:142): He can do Melachah in private. This is why R. Gamliel did not know that R. Yehoshua was a smith until he entered R. Yehoshua's house (Berachos 28a).

Answer #2 (Kesef ha'Kodoshim): Any Melachah that is clearly for a Mitzvah is permitted. The Isur applies only to a peerless judge who rules over the city. This explains how Tana'im and Amora'im engaged in Melachah in public.

Answer #3 (Einayim l'Mishpat ibid.): It is a disgrace to do his own tasks, i.e. that he has no one to serve him. However, earning a living is honorable.

Rema: One may not accept the position if he does not have someone to serve him.

Source (Hagahos Maimoniyos Sanhedrin 8:1): We learn from the Yerushalmi Sof Perek 2 of Sanhedrin.