Silsilat al-Ahadith al-Sahihah

Sayyiduna Abu Umamah (may Allah be pleased with him) narrates that the Messenger of Allah (peace and blessings be upon him) said: "A borrowed item must be returned, and a goat given temporarily for its milk must be returned. Whoever picks up a lost item that is tied with a string or something similar, it is not lawful for him to untie it until he shows it to someone else (and makes him a witness)."

Umayyah bin Safwan bin Umayyah narrates from his father that the Messenger of Allah (peace and blessings be upon him) borrowed some armors from him on the day of Hunayn. He said: O Muhammad! Will they be seized by force? The Prophet (peace and blessings be upon him) said: "No, this is a loan for which compensation will be guaranteed in case of loss."

Ya’la bin Umayyah narrates from his father, who says that the Messenger of Allah (peace and blessings be upon him) said to me: “When my messengers come to you, give them thirty coats of mail and thirty camels.” I said: O Messenger of Allah! If (these things that I am) lending are destroyed, will their value be guaranteed or not? The Prophet (peace and blessings be upon him) said: “If these things remain as they are, then their return is guaranteed, and in case of destruction, there will be no responsibility.”

Saeed bin Abu Saeed narrates from a companion of the Messenger of Allah who heard from the Prophet (peace and blessings be upon him) that he said: "Beware! A loaned item (something taken temporarily) must be returned, a gift given for benefit (for a certain period) must also be returned, a debt must be repaid, and the guarantor of a thing is responsible for its payment."