Musannaf Ibn Abi Shayba 13:1495

Abu Bakr narrated to us, he said: Ibn Idris narrated to us, from Hisham, from Anas ibn Sirin, from Anas ibn Malik, who said: I entrusted six thousand [dirhams], and they were lost. So Umar said to me: "Did anything of yours go with them?" I said: "No." He said: "Then he guaranteed it for me."