Sahih Bukhari
Military Expeditions led by the Prophet (pbuh) (Al-Maghaazi)
Volume: 005 / Book Number: 059 / Hadith Number: 438
Narrated Jabir bin 'Abdullah:
Umar bin Al-Khattab came on the day of Al-Khandaq after the sun had set and he was abusing the infidels of Quraish saying, "O Allah's Apostle! I was unable to offer the ('Asr) prayer till the sun was about to set." The Prophet said, "By Allah, I have not offered this (i.e. 'Asr) prayer." So we came down along with the Prophet to Buthan where he performed ablution for the prayer and then we performed the ablution for it. Then he offered the 'Asr prayer after the sun had set, and after it he offered the Maghrib prayer.