Sahih al-Bukhari 109
Sahih al-Bukhari · Book 3: Knowledge · The sin of a person who tells a lie against the Prophet (saws)
Narrated Salama:
حَدَّثَنَا مَكِّيُّ بْنُ إِبْرَاهِيمَ ، قَالَ حَدَّثَنَا يَزِيدُ بْنُ أَبِي عُبَيْدٍ ، عَنْ سَلَمَةَ ، قَالَ سَمِعْتُ النَّبِيَّ صلى الله عليه وسلم يَقُولُ " مَنْ يَقُلْ عَلَىَّ مَا لَمْ أَقُلْ فَلْيَتَبَوَّأْ مَقْعَدَهُ مِنَ النَّارِ " .
I heard the Prophet (ﷺ) saying, "Whoever (intentionally) ascribes to me what I have not said then (surely) let him occupy his seat in Hell-fire."