Gemara

Question: If one rented a house on the 14th b'Chezkas Baduk (on the pretense that it was checked), and it was found to be unchecked, is this a 'Mekach Ta'os' (a mistaken rental, and the tenant may retract)?

Answer (Abaye): The rental is valid where people themselves check for Chametz, and even in a place where they hire others to check, for people like to do Mitzvos with their own money.

Bava Metzi'a 29b (Shmuel): If one found Tefilin in the market, he estimates their value and may wear them immediately. (If the owner comes and gives a sign, he gives their value to him.)

(Beraisa): One who borrowed a Sefer Torah may not lend it to another.

Question: Why was this taught about a Sefer Torah? It applies to any borrowed object!

Answer: One might have thought that a Sefer Torah is different, for one is happy to do a Mitzvah with his property (i.e. that others use it for a Mitzvah). The Beraisa teaches that this is not so.

Rishonim

Terumas ha'Deshen (100): On Chol ha'Mo'ed, if one does not have his own Arba'ah Minim to bless on, he may take another's Minim. One is Yotzei with borrowed Minim l'Chatchilah. Do not say that he is a Sho'el she'Lo mi'Da'as (one who borrows without permission), and the Rif rules that he is like a Gazlan (robber). Or Zaru'a, Semag, the Rosh, Semak and others disqualify stolen Minim every day. In cases like this, one is happy to do a Mitzvah with his property. The Rosh permits putting on another's Talis without his knowledge. We rely on this, that one is happy to do a Mitzvah with his property. This is when it is evident that there will be no loss to the property. If he found it folded, he must return it folded like it was. If not, the owner is not pleased. If one takes another's Esrog and Lulav to bless on them and wave them properly, surely no one is particular [to object]. This is like a Talis. This is unlike Seforim, for they get dirty and ruined when one learns in them. The Gemara forbids learning in them Stam, i.e. even a little, for there no limit to how much one learns. Putting on a Talis or taking the Minim has a limit. (It is for a short time.) The Mordechai (Bava Metzi'a 262) brings from Avi ha'Ezri that anyone who intends for a Mitzvah is not called a Gazlan, even without permission. Do not learn from there to here. The Mordechai means that the person is not disqualified from swearing (for he does not think that he transgresses). [Perhaps] it is considered stolen, and he is not Yotzei!

Nimukei Yosef (Bava Basra 44b DH Amar ha'Mechaber): Since the Halachah follows Rabanan, that Sho'el she'Lo mi'Da'as is a Gazlan, one may not wear another's Talis or Tefilin without his permission. My Rebbi (the Ritva) permits, since one is happy to do a Mitzvah with his property. I do not understand. One who finds Tefilin may wear them only after estimating their value and buying them for himself! We do not permit due to the Mitzvah! One who borrowed a Sefer Torah may not lend it to another!

Teshuvas Chasam Sofer (1:2): Shitah Mekubetzes (29b) brings from the Ritva that a Sefer Torah, Talis and Tefilin are for the owner himself to use them. If the borrower will wear them out, the owner will be unable to do a Mitzvah later. [He is not happy that others do a Mitzvah if he will lose a Mitzvah.] This does not apply to other cases of monetary loss. This answers the question from Chametz.

Poskim

Shulchan Aruch (OC 14:4): One may take another's Talis and bless on it.

Taz (5): The Rema (649:5) says similarly about a Lulav. The Terumas ha'Deshen equates this to a Talis. However, why do they permit only after the first day? Also Tzitzis is mid'Oraisa, and we rely (on the Chazakah that one is happy to do a Mitzvah with his property) to bless on them without the owner's permission! I answer that there is no Isur Torah to wear a garment without Tzitzis, just there is a Mitzvah to attach Tzitzis on one's garment. There is no Chiyuv here, for it is not his garment. However, above (8:9) we are more stringent about the Berachah than about wearing a garment. One must check the Kashrus of the strings only due to the Berachah. Even though a borrowed Talis is exempt, we say that the owner transfers ownership to the borrower on condition to return it. All the more so, this reasoning allows one to fulfill the Mitzvah of Lulav on the first day with another's Lulav. We can distinguish. On the first day, the Mitzvah is mid'Oraisa, and one is extra particular that his Esrog not become ruined, so we do not rely on 'one is happy to do a Mitzvah with his property'.

Question (Taz 5): Why do we forbid explicitly borrowing another's Lulav on the first day? We should say that people know that one must own it to be Yotzei, and the owner gave a gift on condition to return it! We must say that since the borrower said 'lend', he did not intend for a gift. The Rosh says that when one borrows a Talis with Tzitzis, he must bless, for he intended in a way that it will be his, i.e. a gift on condition to return it. The Rosh says that if one borrowed a ring "in order to be Mekadesh a woman", surely the giver gave it with intent for a way that helps. If a loan does not help, it should be in another way. Not all know the Halachah. We rely on this to say that the Kidushin is Vadai (EH 28:19). If someone else was Mekadesh her afterwards, she does not need a Get from him. All the more so we should rely on this for Esrog on the first day! Esrog is different, for the Torah disqualified a borrowed or stolen Lulav on the first day. Therefore, any expression of borrowing disqualifies. We should not say that he intended for a way that helps. The Torah said not to do so! Regarding Kidushin, logic teaches that one must be Mekadesh with his own property. We must say that the lender intended for a way that helps. However, regarding Tzitzis "Kesuscha" exempts a borrowed garment. This should be like Lulav! Also, if not for "ha'Ezrach", we would have disqualified a borrowed Sukah, since it says "Ta'aseh Lecha." If so, a borrowed Sukah should be Pasul, like a stolen Sukah. This requires great investigation to resolve this. The Rosh allows blessing on a borrowed Talis. I hold like the Maharshal, who disagrees, and all the more so if he borrowed it without the owner's permission.

Rema (649:5): One may take another's Lulav without his knowledge after the first day. One is happy to do a Mitzvah with his property. He (the one taking it) is like a borrower.

Magen Avraham (16): One may not take another's Lulav from his house to the Beis ha'Keneses or vice-versa, like we say [about a Talis] in 14:4.

Taz (7): This is because there is no concern lest it get ruined through his taking and shaking. Therefore, this is unlike learning from another's Seforim, which we forbid, for he (the owner) is concerned lest they get ruined.

Gra (DH u'Mutar): In Bava Metzi'a we do not say [that one is happy to do a Mitzvah with his property]. That is because there is a loss.

Mishnah Berurah (33): On the first day it does not help that he (the owner) is happy, for it must truly belong to you. This is no better than borrowing.

Mishnah Berurah (34): The Pri Megadim permits borrowing it only once. Perhaps the owner objects, so this is forbidden. (For this reason, I say that the borrower should not give to someone else, for perhaps the owner objects.) I wrote (14:13, regarding a Talis) that whenever the owner is there, it is proper to ask permission. We do not rely on the Chazakah when one can easily verify it, and all the more so if one knows that he is particular. Then, letter of the law one may not take without permission.

Kaf ha'Chayim (62): Even according to the opinion that disqualifies a stolen Lulav all seven days, if one took another's against his will with intent to be Yotzei and return it immediately, he is Yotzei with it after the first day. Such a case of borrowing without permission is not considered a Gazlan. He is exempt if Ones occurred. He is unlike a standard borrower without permission, who has monetary benefit from the item. Surely, this is forbidden l'Chatchilah!

Kaf ha'Chayim (61): See what I wrote in Siman 14 [about borrowing a Talis]. The same distinctions apply here.

Kaf ha'Chayim (14:16): If a Talis or Tefilin was left in a locked box, this shows that the owner does not want people to use it. One may not open it with a key to borrow it. The same applies to one who gives it to the Gabai to put away in a locked place. The Gabai may not lend it to another unless he clearly knows that the owner consents.

Kaf ha'Chayim (14:17): One may not borrow it on a Shabbos when everyone gathers to hear the Drashah and it is very crowded and it is prone to get damaged.

Magen Avraham (14:8): Granted, one may borrow another's Talis without his permission, for one is happy that people do a Mitzvah with his property. However, why may he bless? If the owner gave it to him, we can say that it is like a gift on condition to return it. We say so about a Lulav. One may not take without his knowledge. The Rema says about a Lulav. Why may one bless on a Talis without permission? We must say that even though he is exempt [since it is like a borrowed Talis], he may bless if he wants, like women bless on Mitzvas Aseh sheha'Zeman Gerama.