Sahih Bukhari | Volume 4 | Hadith Number 840

Narrated by 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."