Musannaf Ibn Abi Shayba 3:4064

Hushaym narrated to us, he said: 'Abd al-Malik informed us, from 'Ata', that a man prayed the morning prayer with the Prophet, may Allah bless him and grant him peace. When the Prophet finished the prayer, the man stood up and prayed the two rak'ahs. The Prophet, may Allah bless him and grant him peace, said: "What are these two rak'ahs?" He said: "O Messenger of Allah, I came while you were in the prayer, and I had not prayed the two rak'ahs before the dawn, so I disliked praying them while you were praying. When you finished the prayer, I stood and prayed them." The Messenger of Allah, may Allah bless him and grant him peace, laughed, and he did not command him nor did he forbid him.