185: Laws of Borrowing and Renting

One who borrows or rents an animal or movable property from his friend, he is not allowed neither to lend them nor to rent them out to another without the knowledge of the owner. Even sefarim, where there is a mitzvah in lending them out, we do not say that ordinarily it is agreeable to the owners that he should do a mitzvah with their money. Because maybe they don’t want something of theirs in the hand of someone else who isn’t trustworthy in their eyes. But it is permitted for a borrower of a seifer to allow someone else to study in it in his [the borrower’s] home as long as he doesn’t learn alone rather the two of them together. And if it’s is known that it is the owners’ usual way to trust this one [the third part] in matters like this, the borrower is permitted to lend to him, and the rentor to rent [or lend] to him.