Musnad Ahmad 30:120

Al-Walid narrated to us, Al-Awza'i narrated to us, Al-Zuhri narrated to me, from Abu Salamah, from Abu Hurairah, who said: The prayer was established, and the people arranged their rows. The Messenger of Allah (peace and blessings of Allah be upon him) came out and stood in his place. Then he gestured to them with his hand: "Stay where you are." He went out, having performed ghusl (full ablution), and his head was dripping with water, then he led them in prayer.