Sahih al-Bukhari Book 10, Hadith 36
Allah's Messenger (ﷺ) went out (of the mosque) when the Iqama had been pronounced and the rows
straightened. The Prophet (ﷺ) stood at his Musalla (praying place) and we waited for the Prophet (ﷺ) to begin
the prayer with Takbir. He left and asked us to remain in our places. We kept on standing till the
Prophet returned and the water was trickling from his head for he had taken a bath (of Janaba).
My father said, "Allah's Messenger (ﷺ) said, 'If the Iqama is pronounced, then do not stand for the prayer till you see me (in front of you) and do it calmly.' "
Once Iqama was pronounced and the people had straightened the rows, Allah's Messenger (ﷺ) went forward (to lead the prayer) but he was Junub, so he said, "Remain in your places." And he went out, took a bath and returned with water trickling from his head. Then he led the prayer.