Musnad Abu Ya'la al-Mawsili 109:125

Ishaq narrated to us, Waki' narrated to us, Zakariya narrated to us, from al-Sha'bi, from Jabir, that he sold a camel to the Prophet (may Allah bless him and grant him peace), and he stipulated [the condition of] its back [i.e., riding it] until his family.