can only be known in the case of a man whom you have come to know thoroughly and whose regard for you you understand. Examples of this have been reported of a number of people, as illustrated by what the Prophet, peace and blessings be upon him, used to do in the homes of some of his Companions, and by his pledging allegiance on behalf of ʿUthmān, may Allah be pleased with him, while he was absent. Whenever there is doubt about this, borrowing is not permissible.

He also said:

If someone buys an item—a camel or something else—that is being held in safekeeping, then leaves it with the custodian, and the other party subsequently sells it, the second sale is invalid. If the custodian hands it over to the second buyer, its owner—the first buyer—may demand it back from the custodian who handed it over and from the buyer who received it.

He was also asked—may Allah have mercy on him:

Some people entrusted property to a monk in a monastery. He claimed that it had gone missing along with the other contents of the monastery. Then it emerged that he had sold what he claimed had gone missing from the monastery. Must he be held liable for the property or not? Is his word to be accepted? This monk’s monastery stands on the coast of the saltwater sea. He has a brother who is a pirate and takes refuge with him, as do other pirates.