Anas said

When the Prophet (ﷺ) took us out on an expedition against a people he did not set out with us till the morning. He would look at them, and if he heard a call to prayer he refrained from them, but if he did not hear any he attacked them. We went out to Khaibar and reached them by night, but when the morning came and he heard no call to prayer he mounted. I mounted behind Abu Talha and my foot was touching Allah’s Prophet’s They came out to us with their large baskets and their spades, and when they saw the Prophet (ﷺ) they said, “ Muhammad , by Allah, Muhammad and the army," and went for refuge to the fortress. When Allah's Messenger ﷺ saw them he said, “Allah is most great, Allah is most great. Khaibar has fallen.1 When we alight in the courtyard of a people it is an evil morning for those who have been warned."2 1. Or, 'May Khaibar fall. 2. Cf. Al-Qur'an; 37:177. (Bukhari and Muslim.)