Good Manners and Form (Al-Adab)
Ṣaḥīḥ al-Bukhārī 6096
رَأَيْتُ رَجُلَيْنِ أَتَيَانِي قَالاَ الَّذِي رَأَيْتَهُ يُشَقُّ شِدْقُهُ فَكَذَّابٌ يَكْذِبُ بِالْكَذْبَةِ تُحْمَلُ عَنْهُ حَتَّى تَبْلُغَ الآفَاقَ فَيُصْنَعُ بِهِ إِلَى يَوْمِ الْقِيَامَةِ
raʾaytu rajulayni atayānī qālā adh-dhī raʾaytah yushaqqu shidquhu fakadhābun yakdhibu bi-l-kadhbah tuḥmalu ʿanhu ḥattā tablugha al-āfāqa fayuṣnaʿu bihi ilā yawmi al-qiyāmah
Transliteration generated from the Arabic vowel marks
The full narration
Narrated Samura bin Jundub:The Prophet (ﷺ) said, "I saw (in a dream), two men came to me." Then the Prophet (ﷺ) narrated the story (saying), "They said, 'The person, the one whose cheek you saw being torn away (from the mouth to the ear) was a liar and used to tell lies and the people would report those lies on his authority till they spread all over the world. So he will be punished like that till the Day of Resurrection
Source
Ṣaḥīḥ al-Bukhārī · 6096