Musnad Ahmad 30:3588

Uthman ibn Umar narrated to us, Yunus informed us, from al-Zuhri, from Abu Salamah, from Abu Hurairah, who said: The prayer was established and the rows were straightened while we were standing. Then the Messenger of Allah, may Allah bless him and grant him peace, came out to us. When he stood in his place of prayer, he remembered that he was in a state of major ritual impurity (junub). He said to us: "Stay where you are." Then he returned and performed ghusl (ritual bath). Then he came out to us while his head was dripping, and he said the takbir, and we prayed with him.