Sahih Al Bukhari (510)

عن أبي هريرة {أن رسول الله صلى الله عليه وسلم خرج وقد أقيمت الصلاة وعدلت الصفوف حتى إذا قام في مصلاه انتظرنا أن يكبر انصرف قال على مكانكم فمكثنا على هيئتنا حتى خرج إلينا ينطف رأسه ماء وقد اغتسل}

Abu Hurayrah (may Allah be pleased with him) narrated that Allah’s Messenger (peace be upon him) went out (of the mosque) when the Iqamah (the call for starting Salah) had been pronounced and the rows straightened. The Prophet (peace be upon him) stood at his Musalla (praying place) and we waited for the Prophet (peace be upon him) to begin Salah with Takbir (Saying: Allahu Akbar [Allah is the greatest]). He left and asked us to remain in our places. We kept on standing till the Prophet (peace be upon him) returned and the water was trickling from his head for he had taken a bath (for Janabah (the major ritual impurity)).