Gemara

26a (Beraisa): R. Yochanan ben Zakai used to sit in the shade of the Heichal and expound.

(Abaye): He cannot avoid benefit, and he intends to benefit, yet it is permitted!

Rejection (Rava): The walls of the Heichal are for the sake of its inside.

96a - Question: It says "v'Achlu Es ha'Basar ba'Laylah ha'Zeh." Also Pesach Doros is eaten at night!

Answer: "V'Avadta Es ha'Avodah..." [equates Pesach Mitzrayim and Pesach Doros];

"Ha'Zeh" teaches like R. Elazar ben Azaryah, or like R. Akiva.

Berachos 9a (Beraisa - R. Elazar ben Azaryah): It says "v'Achlu Es ha'Basar ba'Lailah ha'Zeh," and "v'Avarti v'Eretz Mitzrayim ba'Lailah ha'Zeh." Just like the latter was at midnight, the [deadline of] the former is at midnight;

R. Akiva says, the Korban Pesach is eaten "b'Chipazon" (in haste), i.e. until the time of haste (dawn, when Mitzrayim compelled Yisrael to leave).

Other Tana'im argue as R. Elazar and R. Akiva do;

(Beraisa - R. Eliezer): "Sham Tizbach Es ha'Pesach ba'Arev k'Vo ha'Shemesh Mo'ed Tzeischa mi'Mitzrayim" -- you slaughter in the Erev (afternoon), you eat k'Vo ha'Shemesh (at night), and you burn (leftovers) at Mo'ed Tzeischa mi'Mitzrayim (in the morning);

R. Yehoshua says, you slaughter ba'Erev, and you eat from k'Vo ha'Shemesh until Mo'ed Tzeischa mi'Mitzrayim (morning).

Avodah Zarah 43b (Mishnah - R. Yosi): One grinds up (idols) and throws the dust to the wind or casts it to the sea.

Chachamim: No, this will fertilize the ground. We may not derive any benefit from idols - "Lo Yidbak b'Yadcha Me'umah Min ha'Cherem."

(Beraisa - R. Yosi): "... Ha'Egel Lakachti... va'Ashlich Es Afaro El ha'Nachal." (Moshe threw the dust of the golden calf to the river, even though it will be deposited on the banks!)

Bava Metzi'a 70b (Rav Nachman): "Marbeh Hono b'Neshech l'Chonen Dalim Yikbetzenu" - one who lends even to a Nochri on Ribis will lose his money.

Question (Rava) Suggestion: We read "la'Nochri Sashuch (you will take Ribis from him)"!

Answer: No, we read "Sashich" (you will pay Ribis to him).

Question (Mishnah): We may borrow from or lend to a Nochri or Ger Toshav on Ribis.

Answer #1 (R. Chiya brei d'Rav Huna): The Mishnah permits only if he needs it to survive.

Answer #2 (Ravina): The Mishnah permits only a Chacham;

Rav Nachman forbids lending to a Nochri on Ribis lest one learn from his deeds. A Chacham would not learn from his deeds.

Sanhedrin 19a (Mishnah): A king does not judge [and is not judged].

(Rav Yosef): This applies only Malchei Yisrael (the 10 tribes). Kings of Beis David judge and are judged - "Beis David... Dino la'Boker Mishpat."

Once, Shimon ben Shetach was judging Yanai. He told him to stand.

Yanai: I will not listen to you, rather, to the other judges.

The other judges feared Yanai. Hash-m killed them all. They enacted that Malchei Yisrael do not judge, and we do not judge them.

Rishonim

Rambam (Hilchos Malveh 5:1): It is a Mitzvas Aseh to lend to a Nochri with Ribis - "l'Nochri Sashich."

Rambam (2): Chachamim forbid lending to a Nochri with fixed Ribis above what is needed for income, lest one learn from his deeds due to dwelling so much with him. A Chacham may lend to him even for profit, since he is not prone to learn from his ways! Anyone may lend to him with Avak (mid'Rabanan) Ribis.

Tosfos (70b DH Tashich): If we read Lo Tashuch, we understand why it is obligatory. One may not give gifts to Nochrim. What was the question from the verse? The Isur to lend to them is only a decree mid'Rabanan! I answer that since the verse says to take Ribis from them, Chachamim should not have forbade. We bring the verse from Shlomo, for perhaps he decreed. Alternatively, he discussed Torah Ribis, and Chachamim supported their decree from his verse. R. Tam says that nowadays the custom is to lend to Nochrim because we follow the lenient opinion for mid'Rabanan laws. We hold like the version that they never forbade. Even according to Version #1, we can permit nowadays, for due to taxes of the king and nobles, all is needed for our livelihood. Alternatively, we have no other income, so it is not forbidden more than other business with them.

Rashi (Bava Metzi'a 71a DH bi'Chdei): Chachamim permitted [lending to Nochrim with Ribis] what is needed for income. Above this is forbidden mid'Rabanan, lest one come l'Misrach (get used to this, and lend to Yisre'elim with Ribis).

Chasam Sofer (YD 106): The Taz (brought below) says that Chachamim cannot forbid what the Torah explicitly permitted. The Isur to lend to Nochrim would be difficult for the Taz had Chachamim forbade due to taking Ribis. However, they forbid lest one learn from Nochrim's ways! The Torah is still fulfilled when there is no concern for being drawn after their ways, e.g. a Chacham. One can challenge me from Rashi, but one can resolve this easily.

Note: One could explain "l'Misrach" to mean that he will constantly deal with Nochrim, and learn from their ways. However, the Chasam Sofer's coming words connote that Rashi explained R. Chiya brei d'Rav Huna before the Gemara answered that we forbid lending to a Nochri on Ribis lest one learn from his deeds.

Chasam Sofer (ibid.): People challenged the Rambam, who say that there is a Mitzvas Aseh to take Ribis from Nochrim. The Gemara said that the verse only forbids taking Ribis from a Yisrael with a Lav and an Aseh! The Ran says that in the conclusion, that the Isur is mid'Rabanan, we return to the initial assumption that it is an Aseh. The Shlah says similarly. The Lechem Mishneh disagrees. Surely the questioner knew that the Isur is only mid'Rabanan! Even so, he asked, for since it is a Torah Aseh, how could Chachamim forbid it? If so, also the conclusion holds that it is not a Torah Aseh. I answer that the Hava Amina was that Chachamim totally forbade, even what is needed for income or for a Chacham, lest he transgress Ribis [with a Yisrael]. The Gemara asked how Chachamim could forbid a Torah Aseh. The Gemara concluded that they forbade lest one learn from the Nochri, and permitted for his needed income and for a Chacham, so this is not difficult. The Rambam properly calls it an Aseh. Another answer for the Taz is that the Torah did not command to lend to Nochrim in order to take Ribis. Rather, if we lend, we must take Ribis. The Torah did not discuss not lending to them at all. Indeed, if one must lend to them, Chachamim did not uproot the Torah obligation to take Ribis from them.

Tosfos (26a DH She'ani): Rashi says that shade of the Heichal is permitted, for it is not Derech Hana'ah. The Torah forbids (a Zar or Tamei) to eat Terumah, therefore we forbid only Derech Hana'ah, and we learn Me'ilah from Terumah. One may not sit under an Asherah (Avodah Zarah 48b) because this is Derech Hana'ah. Also, the Isur of idolatry does not mention eating.

Sha'ar ha'Melech (Hilchos Yesodei ha'Torah 5:8): Tosfos' first answer connotes that the Torah permits Lo Derech Hana'ah even regarding idolatry. Avodah Zarah 43b connotes that the Torah forbids it! If not, what was the proof from Moshe? Chachamim did not decree yet! Perhaps R. Yosi holds that since it says "va'Ashlich Es Afro", Chachamim cannot forbid this, like the Taz says. However, Chavos Ya'ir refuted the Taz. In Bava Metzi'a we challenge a decree [not to lend to Nochrim on Ribis] from a verse. This seems like the Taz. However, there is different, for it is a Mitzvah [to take Ribis from them], therefore Chachamim cannot decree. (Note: Chachamim can decree to passively be Mevatel Mitzvos, e.g. Lulav on Shabbos! Perhaps he means that they cannot totally nullify a Mitzvah.) Tosfos (70b DH Tashich) says so. Tosfos in Kesuvos (51b DH Ones) connotes like the Taz, and also Tosfos in Chulin (12a DH Pesach).

Poskim

Shulchan Aruch (CM 2:1): Any Beis Din, if it sees the nation wantonly sin, can give a capital, monetary or other punishment to fence this.

Taz (DH Tu Isa): [The Tur and Rambam bring from Yevamos 90b] "Chachamim may punish one who is not liable, not to transgress Torah, [rather, for a fence]." Why would we think that they may transgress Torah? Rather, even though they may forbid what the Torah permits, this is not for what a verse explicitly permits, e.g. Hana'ah from Chelev.

Tzlach (Berachos 9a DH v'Ad): Based on the Taz, according to R. Yehoshua, the Torah explicitly permits until dawn, so Chachamim could not forbid after midnight. [R. Eliezer and] R. Akiva hold that the verse discusses the time they were rushed, which was only in Mitzrayim, so Chachamim could decree.

Kesef Mishneh (Hilchos Melachim 3:7): They decreed not to judge Malchei Yisrael due to an episode with Yanai. This does not depend on whether the king is from Beis David or Yisrael, rather, on whether he is a Tzadik or Rasha! What do we learn from the verse? If it means that we judge only Malchei Beis David, why did they judge Yanai? Rather, since the verse discusses judging Malchei Beis David, even though a mishap occurred, Chachamim would not decree unlike the verse. Therefore, they decreed [when there were no Malchei Beis David] with intent that it not affect future Malchei Beis David.

Sha'ar ha'Melech (ibid.): Shitah Mekubetzes on Sanhedrin (brought in Sefer Chamra v'Chayei) asks how we learn from "Dino l'Boker Mishpat" that kings of Beis David judge and are judged. This verse preceded the episode with Yanai, due to which they decreed not to judge Malchei Yisrael! He answered that since Hash-m commanded, Chachamim would not decree against it.

Chasam Sofer (YD 117:1): The Kesef Mishneh already said so [like the Taz] in Hilchos Melachim 3:7.