Sunan an-Nasa'i, Book 37, Hadith 98 (In-Book) ⓘ
It was narrated that Al-Hasan said: "The Messenger of Allah [SAW] said: 'Whoever changes his religion, kill him.'"
أَخْبَرَنَا مُوسَى بْنُ عَبْدِ الرَّحْمَنِ، قَالَ حَدَّثَنَا مُحَمَّدُ بْنُ بِشْرٍ، قَالَ حَدَّثَنَا سَعِيدٌ، عَنْ قَتَادَةَ، عَنِ الْحَسَنِ، قَالَ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم " مَنْ بَدَّلَ دِينَهُ فَاقْتُلُوهُ " . قَالَ أَبُو عَبْدِ الرَّحْمَنِ وَهَذَا أَوْلَى بِالصَّوَابِ مِنْ حَدِيثِ عَبَّادٍ .
also referenced under: Hadith 4063 (Reference) & Volume 5, Book 37, Hadith 4068 (DarusSalam)