From Anas ibn Malik (may Allah be pleased with him), who said: We got to Khaybar early in the morning, and the inhabitants were coming out with their shovels, and when they saw the Prophet (SAW) they said: Muhammad, by Allah! Muhammad and his army! And the Prophet (SAW) said: Allah is bigger [Allahu akbar]! Khaybar is ruined! Indeed when we descend onto a people, the morning gets bad for those who have been warned! Then we came across some donkey meat, but the Prophet’s (SAW) proclaimer announced: Indeed Allah and his Messenger prohibit you from eating donkey meat, for truly it is a filthy thing.
- Sahih Al-Bukhari, The book of military raids

His words “Khaybar is ruined!” added as extra support in jihad: He raised his hands and said “Allahu Akbar! Khaybar is ruined!”. The addition of takbir [“Allahu akbar”] is in most of the narrations from Anas and Humaid. Al-Suhaili said: Saying this conveyed optimism, for when He (SAW) saw implements of destruction – even though saying “shovel” is like saying “I dug” or “I scraped” – He took it to mean that their city would be destroyed. (end quote). And so it is implied that He said “Khaybar is destroyed” by way of divine inspiration, and what He said after that supported this: “Indeed when we descend onto a people, the morning gets bad for those who have been warned”.