كتاب البر والصلة والآداب
45  
The Book of Virtue, Enjoining Good Manners, and Joining of the Ties of Kinship
(26)
Chapter: Criticism Of The One Who Is Two-Faced, And The Prohibition Of Doing That
(26)
باب ذَمِّ ذِي الْوَجْهَيْنِ وَتَحْرِيمِ فِعْلِهِ ‏‏
Sahih Muslim 2526 c

Abu Huraira reported Allah's Messenger (ﷺ) as saying:

The worst amongst the people is the double-faced one; he comes to some people with one face and to others with the other face.
حَدَّثَنَا يَحْيَى بْنُ يَحْيَى، قَالَ قَرَأْتُ عَلَى مَالِكٍ عَنْ أَبِي الزِّنَادِ، عَنِ الأَعْرَجِ، عَنْ أَبِي هُرَيْرَةَ، أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم قَالَ ‏ "‏ إِنَّ مِنْ شَرِّ النَّاسِ ذَا الْوَجْهَيْنِ الَّذِي يَأْتِي هَؤُلاَءِ بِوَجْهٍ وَهَؤُلاَءِ بِوَجْهٍ ‏"‏ ‏.‏
Reference : Sahih Muslim 2526c
In-book reference : Book 45, Hadith 127
USC-MSA web (English) reference : Book 32, Hadith 6300
  (deprecated numbering scheme)