Sahih al-Bukhari Book 10, Hadith 38
On the day of Al-Khandaq (the trench), `Umar bin Al-Khattab went to the Prophet (ﷺ) and said, "O
Allah's Messenger (ﷺ)! By Allah, I could not pray (the `Asr) till the sun had set." `Umar told this to the
Prophet at the time when a fasting person had done Iftar (taken his meals). The Prophet (ﷺ) then went to
Buthan and I was with him. He performed ablution and offered the `Asr prayer after the sun had set
and then the Maghrib prayer.
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.
Once the Iqama was pronounced and the Prophet (ﷺ) was talking to a man (in a low voice) in a corner of the mosque and he did not lead the prayer till (some of) the people had slept (dozed in a sitting posture) .