Sayyiduna Ibn Abbas (may Allah be pleased with them both) narrates: I spent the night with the Messenger of Allah (peace and blessings be upon him). He ((peace and blessings be upon him)) got up, performed ablution, then prayed two rak'ahs at a time until they came to ten rak'ahs, then he prayed three rak'ahs of witr, then he lay down and slept until he began to snore; his sleep was recognised by his snoring. Then the mu'adhdhin called him for the Fajr prayer, so he ((peace and blessings be upon him)) came out and led the prayer without performing ablution.
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 12120