Musnad Ahmad 33:944

Yazid narrated to us, Sufyan—meaning al-Thawri—informed us, from Abu al-Zubayr, from Jabir, who said: The Prophet, peace and blessings of Allah be upon him, sent me for a need. I came while he was riding his mount, and his face was toward the east, and he was gesturing with gestures. I spoke to him, but he did not reply to me. When he finished, he said: "I was praying."