The Prophet ﷺ set out for Khaibar and reached it at night. He used not to attack if he reached the people at night, till the day broke. So, when the day dawned, the Jews came out with their bags and spades. When they saw the Prophet; they said, "Muhammad and his army!" The Prophet ﷺ said, Allahu--Akbar! (Allah is Greater) and Khaibar is ruined, for whenever we approach a nation (i.e. enemy to fight) then it will be a miserable morning for those who have been warned." (Using translation from Bukhārī 2945)  

أَنَّ رَسُولَ اللهِ ﷺ خَرَجَ إِلَى خَيْبَرَ أَتَاهَا لَيْلًا وَكَانَ إِذَا أَتَى قَوْمًا بِلَيْلٍ لَمْ يُغِرْ عَلَيْهِمْ حَتَّى يُصْبِحَ فَخَرَجَتْ يَهُودٌ بِمَسَاحِيهِمْ وَمَكَاتِلِهِمْ فَلَمَّا رَأَوْهُ قَالُوا مُحَمَّدٌ وَاللهِ مُحَمَّدٌ وَالْخَمِيسُ فَقَالَ رَسُولُ اللهِ ﷺ «اللهُ أَكْبَرُ خَرِبَتْ خَيْبَرُ إِنَّا إِذَا نَزَلْنَا بِسَاحَةِ قَوْمٍ فَسَاءَ صَبَاحُ الْمُنْذَرِينَ»