Musnad Ahmad 1119:10

Zakariya ibn 'Adi narrated to us, he said: 'Ubayd Allah ibn 'Amr al-Raqqi informed us, from Ishaq ibn Rashid, from 'Abd al-Hamid ibn 'Abd al-Rahman ibn Zayd ibn al-Khattab, from 'Awf ibn Malik, he said: I came to the Messenger of Allah, may Allah bless him and grant him peace, at Tabuk at the end of the dawn, and he was in a tent, or he said: a dome made of tanned leather. He said: So I asked, then I sought permission, and I said: "May I enter?" He said: "Enter." I said: "All of me?" He said: "All of you." He said: So I entered, and behold, he was performing ablution with a measured, deliberate ablution.