Musnad Ahmad 1153:1773

Waki’ narrated to us, from Isra’il, from Abu Ishaq, from al-Aswad, who said: I said to ‘Aishah: "Inform me about the prayer of the Messenger of Allah (peace and blessings of Allah be upon him)?" She said: "The Messenger of Allah (peace and blessings of Allah be upon him) used to sleep during the first part of it, and stand during the last part of it. When he stood, he would perform ablution and pray what Allah the Almighty had decreed for him. If he had a need for his wife, he would go to his wife; otherwise, he would incline toward his bed. If he had gone to his wife, he would sleep in his state without touching water, until, when it was the time of the first call (Adhan), he would spring up—by Allah, she did not say 'stood up'—and if he was in a state of major ritual impurity (junub), he would pour water over himself—by Allah, she did not say 'performed ghusl'—and otherwise, he would perform his ablution for prayer, then pray two rak'ahs, then go out to the mosque."