(25) باب إِذَا قَالَ الإِمَامُ مَكَانَكُمْ. حَتَّى رَجَعَ انْتَظَرُوهُ
Narrated Abu Huraira:
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.
Reference: Sahih al-Bukhari 640
In-book reference: Book 10, Hadith 37
USC-MSA web (English) reference(deprecated numbering scheme): Vol. 1, Book 11, Hadith 613