Musannaf Ibn Abi Shaybah

Hazrat Hakam (may Allah have mercy on him) says that if a person had a debt upon another and he gifted his debt to him, then he no longer has the right to take it back.

Hazrat Shu’bah, may Allah have mercy on him, says that Hazrat Hakam said to me: Ibn Abi Layla came to me and asked, “A person had a debt upon another, and he gifted it to him. Can he take it back?” I replied, “No.” I asked Hazrat Hammad, and he said, “Why not? He can take it back.”