Musannaf Ibn Abi Shayba 13:1240

Abu Bakr narrated to us, he said: Ibn Abi Za'idah narrated to us, from Zakariya, from al-Sha'bi, from Jabir ibn Abdullah, that he sold a camel to the Prophet, peace and blessings of Allah be upon him, and stipulated [the condition of] its back [i.e., riding it] to Medina.