Musnad Ahmad 25:700

'Abd al-Razzaq narrated to us, he said: Sufyan informed us, from Salamah ibn Kuhayl, from Kurayb, from Ibn 'Abbas, who said: I slept at the house of my maternal aunt, Maymunah bint al-Harith. The Prophet, peace and blessings of Allah be upon him, stood up during the night and went to relieve himself. Then he came and washed his face and his hands, then he slept. Then he stood up during the night and went to the water skin and untied its strap, and he performed ablution, a moderate ablution, not excessive, yet he was thorough. Then he stood to pray. I stretched, disliking that he should see me, for I was keeping watch over him. Then I stood up and did as he had done. I stood to his left, so he took hold of what was next to my ear and turned me around until I was on his right. He prayed, and his prayer was completed at thirteen rak'ahs, including the two rak'ahs of Fajr. Then he lay down and slept until he breathed heavily. Then Bilal came and informed him of the prayer, so he stood up and prayed without performing ablution.