Sahih al-Bukhari 4208
Sahih al-Bukhari · Book 64: Military Expeditions led by the Prophet (pbuh) (Al-Maghaazi) · Ghazwa of Khaibar
Narrated Abu `Imran:
حَدَّثَنَا مُحَمَّدُ بْنُ سَعِيدٍ الْخُزَاعِيُّ ، حَدَّثَنَا زِيَادُ بْنُ الرَّبِيعِ ، عَنْ أَبِي عِمْرَانَ ، قَالَ نَظَرَ أَنَسٌ إِلَى النَّاسِ يَوْمَ الْجُمُعَةِ، فَرَأَى طَيَالِسَةً فَقَالَ كَأَنَّهُمُ السَّاعَةَ يَهُودُ خَيْبَرَ.
Anas looked at the people wearing Tailsans (i.e. a special kind of head covering worn by Jews in old days). On that Anas said, "At this moment they (i.e. those people) look like the Jews of Khaibar."