Virtues and Merits of the Prophet (pbuh) and his Companions

Bukhari :: Book 4 :: Volume 56 :: Hadith 840

Narrated Anas bin Malik:

Allah's Apostle reached Khaibar in the early morning and the people of Khaibar came out with their spades, and when they saw the Prophet they said, "Muhammad and his army!" and returned hurriedly to take refuge in the fort. The Prophet raised his hands and said, "Allah is Greater! Khaibar is ruined ! If we approach a nation, then miserable is the morning of those who are warned."