Musnad Ahmad 27:647

Ibrahim ibn Habib ibn al-Shahid narrated to us, my father narrated to us, from Anas ibn Sirin, who said: I said to Abdullah ibn Umar, "Should I recite behind the Imam?" He said, "The recitation of the Imam is sufficient for you." I said, "The two rak'ahs of the dawn (Fajr), should I lengthen the recitation in them?" He said, "The Messenger of Allah (peace and blessings of Allah be upon him) used to pray the night prayer two by two." I said, "I only asked you about the two rak'ahs of the dawn." He said, "You are indeed thick-headed. Do you not see me beginning the hadith: 'The Messenger of Allah (peace and blessings of Allah be upon him) used to pray the night prayer two by two, and when he feared the morning, he would perform witr with one rak'ah, then he would lay his head down'?" If you wish, you may say he slept, and if you wish, you may say he did not sleep. "Then he would stand for them (the two rak'ahs of dawn) while the adhan was in his ears." So what length could there be then? I said, "A man bequeathed wealth in the way of Allah; should it be spent on Hajj?" He said, "If you were to do that, it would be from the way of Allah." I said, "A man misses a rak'ah with the Imam, and the Imam gives the taslim; should he stand to make it up before the Imam stands?" He said, "When the Imam gave the taslim, he would stand." I said, "A man takes on debt more than his wealth?" He said, "Every treacherous person will have a banner on the Day of Resurrection at his buttocks, according to the extent of his treachery."