Musannaf Ibn Abi Shayba 13:1766

Abu Bakr narrated to us, he said: Jarir narrated to us, from Mughira, from Ibrahim, regarding a man who has a pledge (rahn) with a man, and he says: "If I do not bring you [the debt] by such and such [time], then it is yours." He said: "The pledge does not become forfeited (la yughlaq)." And [regarding the saying]: "If I do not bring you [the debt] by such and such [time], then sell it and take what is yours," he said: "He cannot be the trustee of himself, nor can his sale [be valid]."