Musnad Ahmad 33:105

Abdullah narrated to us: Ali ibn Hakim al-Awdi and Abu Bakr ibn Abi Shaybah narrated to us, they said: Sharik narrated to us, from Salamah ibn Kuhayl, from Abu al-Zubayr, from Jabir: "That the Prophet, peace and blessings of Allah be upon him, sold the mudabbar (a slave promised freedom upon the master's death)."