Military Expeditions led by the Prophet (pbuh) (Al-Maghaazi)
Bukhari :: Book 5 :: Volume 59 :: Hadith 508
Narrated Suwaid bin An-Numan:
I went out in the company of the Prophet in the year of Khaibar, and when we reached As Sahba' which is the lower part of Khaibar, the Prophet offered the Asr prayer and then asked the people to collect the journey food. Nothing was brought but Sawiq which the Prophet ordered to be moistened with water, and then he ate it and we also ate it. Then he got up to offer the Maghrib prayer. He washed his mouth, and we too washed our mouths, and then he offered the prayer without repeating his abulution.