Musnad Ahmad 32:1270

'Abd al-Samad narrated to us, Hammad narrated to us, Thumamah narrated to me, from Anas ibn Malik, that the companions of the Messenger of Allah (may Allah bless him and grant him peace) came to him one night in Ramadan. He prayed for them and made it light. Then he entered and prolonged the prayer. Then he came out and prayed with them, then he entered and prolonged the prayer. He did that repeatedly. When morning came, they said: "O Messenger of Allah, we came to you and you did such and such." He said: "It was for your sake that I did that."