Sahih al-Bukhari 6047
Narrated Thabit bin Ad-Dahhak:
(who was one of the companions who gave the pledge of allegiance to the Prophet (ﷺ) underneath the tree 
(Al-Hudaibiya)) Allah's Messenger (ﷺ) said, "Whoever swears by a religion other than Islam (i.e. if 
somebody swears by saying that he is a non-Muslim e.g., a Jew or a Christian, etc.) in case he is 
telling a lie, he is really so if his oath is false, and a person is not bound to fulfill a vow about a thing 
which he does not possess. And if somebody commits suicide with anything in this world, he will be 
tortured with that very thing on the Day of Resurrection; And if somebody curses a believer, then his 
sin will be as if he murdered him; And whoever accuses a believer of Kufr (disbelief), then it is as if 
he killed him."
حَدَّثَنَا مُحَمَّدُ بْنُ بَشَّارٍ، حَدَّثَنَا عُثْمَانُ بْنُ عُمَرَ، حَدَّثَنَا عَلِيُّ بْنُ الْمُبَارَكِ، عَنْ يَحْيَى بْنِ أَبِي كَثِيرٍ، عَنْ أَبِي قِلاَبَةَ، أَنَّ ثَابِتَ بْنَ الضَّحَّاكِ، وَكَانَ، مِنْ أَصْحَابِ الشَّجَرَةِ حَدَّثَهُ أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم قَالَ ‏
"‏ مَنْ حَلَفَ عَلَى مِلَّةٍ غَيْرِ الإِسْلاَمِ فَهْوَ كَمَا قَالَ، وَلَيْسَ عَلَى ابْنِ آدَمَ نَذْرٌ فِيمَا لاَ يَمْلِكُ، وَمَنْ قَتَلَ نَفْسَهُ بِشَىْءٍ فِي الدُّنْيَا عُذِّبَ بِهِ يَوْمَ الْقِيَامَةِ، وَمَنْ لَعَنَ مُؤْمِنًا فَهْوَ كَقَتْلِهِ، وَمَنْ قَذَفَ مُؤْمِنًا بِكُفْرٍ فَهْوَ كَقَتْلِهِ ‏"‏‏.‏