Musnad Abu Ya'la al-Mawsili 129:97

Masruq ibn al-Marzuban narrated to us, Yahya ibn Zakariyya narrated to us, from Humayd, from Anas, who said: The Messenger of Allah (may Allah bless him and grant him peace) said: "When one of you comes to the prayer, let him walk at his ease. Let him pray what he catches, and let him complete what he missed."