Musnad Ahmad 32:1614

Ali ibn Asim narrated to us, from Humayd, from Anas, and Khalid, from Muhammad, from Abu Hurayrah, that the Prophet (peace and blessings of Allah be upon him) said: "When one of you comes and the prayer has been established, let him walk at his ease, and let him pray what he catches, and let him complete what he missed."