Musnad Ahmad 33:377

Abu al-Nadr and Hasan ibn Musa narrated to us, they said: Zuhayr narrated to us, Abu al-Zubayr narrated to us—Hasan said in his narration: From Abu al-Zubayr, from Jabir, who said: The wife of Bashir said: "Give my son your slave as a gift, and have the Messenger of Allah (peace and blessings of Allah be upon him) bear witness for me." He said: So he came to the Messenger of Allah (peace and blessings of Allah be upon him) and said: "The daughter of so-and-so asked me to give her son my slave as a gift, and she said: 'Have the Messenger of Allah (peace and blessings of Allah be upon him) bear witness for me.'" He said: "Does he have brothers?" He said: "Yes." He said: "And have you given all of them the same as what you gave him?" He said: "No." He said: "This is not appropriate, and I do not bear witness except to what is right."