Siman 342

A borrower is not permitted to lend to another even within the days of his borrowing, and even if he borrowed a Sefer Torah, whereby he performs a mitzvah by lending it to another, and presumably a person is pleased that a mitzvah be performed with his property; nevertheless, he is not permitted to lend it to others, for we do not say this reasoning except regarding a minor matter and not regarding books, which are prone to be damaged through their study, as was written in Orach Chaim siman 14. Therefore, to lend it to them to look into them alone and not to study with diligence is permitted [it appears to me]. And when he lent to others unlawfully and they were damaged while with the other, even if it was damaged due to work, he is liable, unless he has proof with which he could be exempt had it been in his hand—that if he had performed the work, it would have been damaged as well. And he must bring witnesses that it was damaged due to the work, or he must swear to this. But the second person, to whom the borrower lent it, is not believed with his oath unless the lender was also accustomed to lending to this person, for then he cannot say "I do not believe him with an oath" [Shach], as was written in siman 291 section 48. And even if he is not accustomed to lending to him but only to depositing with him, he is also exempt based on the oath of the second person, for he cannot say that he is not trusted to him with an oath, for what difference is there to me between a shomer's oath or a borrower's oath [ibid.]. And when he is liable to pay because he lent to another, his liability takes effect upon him from the time of his lending to the other; and even according to the opinion of the Tur that was explained in siman 341 section 5, that the liability takes effect only from the time of the unavoidable accident, nevertheless here, where he acted unlawfully, his liability takes effect from the time of the lending [it appears to me, and see Ketzot HaChoshen].

Our teacher, the Rema, wrote that a thing which is impossible to smuggle away or to deny, such as a house or a ship, it is permitted to lend. Thus far his words. For he holds that the reason the borrower is not permitted to lend is perhaps he will smuggle it away and deny it, and he compares this to one who rents a house, who is permitted to rent it to another who is like him, as is written in siman 316, see there. And according to this, the reason is simple for what he wrote in section 1, that even books he is not permitted to lend to another. And one should ask regarding this: behold, even a watchman is forbidden to hand over to another watchman for other reasons, as is written in siman 291, and all the more so that a borrower is forbidden to hand over the use to another borrower [and so it appears from Rashi, Bava Metzia 29b]. And from this there was a proof for what was written there, that if his desire is to pay when the second party is unable to bring witnesses, that it is permitted even ab initio; but it has already been explained there that regarding a borrower, it is certainly forbidden ab initio. And from one who rents a house there is no proof, for certainly since he paid the rent and he does not need it, he is permitted to rent it to another so that he does not lose his money; but regarding a borrower who pays nothing, why should he lend it to another without the owner's knowledge? And the opinion of our teacher, the Rema, appears to be that since in the Gemara both are stated in one phrasing—"the borrower is not permitted to lend and the renter is not permitted to rent"—just as regarding a renter of a house it was permitted for him to rent it to another, so too regarding a borrower of a house, because all the days of his borrowing it is as if acquired to him, for from this reason the heirs use it all the days of its borrowing, as is written in siman 341. And according to this, this law that the borrower is not permitted to lend applies only to movables. Nevertheless, the essence of the matter is puzzling, for in the Gemara [Bava Metzia 36a] regarding a watchman who handed over to a watchman, two reasons were stated: one because "it is not my will that my deposit be in the hand of another," and because he is not trusted by him for an oath; but this reason of "perhaps he will smuggle it away" we have not found. And if we say that this reason of "it is not my will that my deposit be in the hand of another" is because of the reason "perhaps he will smuggle it away"—behold, for the law we rule according to the second reason, as is written in siman 291. And in the responsa of the Rashba brought by our teacher, the Beit Yosef, it implies that specifically when the owners are with them, see there; and it requires further study for the law. And a watchman who lent or rented to another, he has committed misappropriation and is liable for accidents, as is written there.