Musannaf Ibn Abi Shayba 3:6130

Waki’ narrated to us, he said: Sufyan narrated to us, from Abu al-Zubayr, from Jabir, who said: The Prophet (may Allah bless him and grant him peace) sent me for a need. He said: So I came to him while he was praying upon his riding beast facing the east, and the prostration was lower than the bowing.