From Sahih Muslim (Hadith 1800):
Ibn `Abbas reported:I spent a night in the house of my mother's sister Maimuna. The Apostle of Allah (ﷺ) got up for observing voluntary prayer (Tahajjud) at night. The Apostle of Allah (ﷺ) stood by the water-skin and performed ablution and then stood up and prayed. I also got up when I saw him doing that. I also performed ablution from the water-skin and then stood at his left side. He took hold of my hand from behind his back and then turned me from his back to his right side. I (`Ata', one of the narrators) said: Did it concern the voluntary prayer (at night)? He (Ibn `Abbas) said: Yes
Reference: Muslim 1800