Musannaf Ibn Abi Shayba 3:5032

Abu Bakr narrated to us, he said: Yahya ibn Ya'la narrated to us, from Uthman ibn al-Aswad, who said: We visited Mujahid, I and a companion of mine, and the prayer time arrived. He said: "Go and pray, and walk at your ease (leisurely). Whatever you catch with the Imam, pray it, and whatever you miss, complete it."