Sahih Bukhari Volume 007, Book 065, Hadith Number 296.
Narrated By Suwaid bin An-Nu'man : We went out with Allah's Apostle to Khaibar, and when we were at As-Sahba', (Yahya, a sub-narrator said, "As-Sahba' is a place at a distance of one day's journey to Khaibar)." Allah's Apostle asked the people to bring their food, but there was nothing with the people except Sawiq. So we all chewed and ate of it. Then the Prophet asked for some water and he rinsed his mouth, and we too, rinsed our mouths. Then he led us in the Maghrib prayer without performing ablution (again).