Abu Dawud Book 1, Hadith Number 201.

Chapter : Performing ablution after awaking from sleep.

Narated By Anas b. Malik : (The people) stood up for the night prayer and a man stood up and spoke forth Apostle of Allah, I have to say something to you. He (the Prophet) entered into secret conversation with him, till the people or some of the people dozed off, and then he led them in prayer. He (Thabit al-Bunani) did not mention ablution.