Good Manners and Form (Al-Adab)
Ṣaḥīḥ al-Bukhārī 6178
إِنَّ الْغَادِرَ يُنْصَبُ لَهُ لِوَاءٌ يَوْمَ الْقِيَامَةِ، فَيُقَالُ هَذِهِ غَدْرَةُ فُلاَنِ بْنِ فُلاَنٍ
inna al-ghādira yunṣabu lah liwāʾun yawma al-qiyāmah, fayuqālu hadhihi ghadrah fulāni bni fulānin
Transliteration generated from the Arabic vowel marks
The full narration
Narrated Ibn `Umar:Allah's Messenger (ﷺ) said, "A flag will be fixed on the Day of Resurrection for every betrayer, and it will be announced (publicly in front of everybody), 'This is the betrayal (perfidy) so-and-so, the son of so-and-so
Source
Ṣaḥīḥ al-Bukhārī · 6178
Ṣaḥīḥ