Musnad Ahmad 32:975

Bahz ibn Asad narrated to us, Hammad narrated to us, Thumamah ibn Abdullah ibn Anas informed us, 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. He went out and prayed with them, and he made it light. Then he entered his house and made it long. Then he went out and prayed with them, and he made it light. Then he entered his house and made it long. When morning came, they said: "O Messenger of Allah, you prayed, and you would make it long when you entered your house, and you would make it light when you went out." He said: "It was for your sake that I did that."