Sunan an-Nasa'i, Hadith 4062 ⓘ
It was narrated that Ibn 'Abbas said: "The Messenger of Allah [SAW] said: 'Whoever changes his religion, kill him.'"
أَخْبَرَنِي هِلاَلُ بْنُ الْعَلاَءِ، قَالَ حَدَّثَنَا إِسْمَاعِيلُ بْنُ عَبْدِ اللَّهِ بْنِ زُرَارَةَ، قَالَ حَدَّثَنَا عَبَّادُ بْنُ الْعَوَّامِ، قَالَ حَدَّثَنَا سَعِيدٌ، عَنْ قَتَادَةَ، عَنْ عِكْرِمَةَ، عَنِ ابْنِ عَبَّاسٍ، قَالَ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم " مَنْ بَدَّلَ دِينَهُ فَاقْتُلُوهُ " .
also referenced under: Book 37, Hadith 97 (In-Book) & Volume 5, Book 37, Hadith 4067 (DarusSalam)