Sunan an-Nasa'i, Volume 5, Book 37, Hadith 4069 (DarusSalam) ⓘ
It was narrated from Anas that : Ibn 'Abbas said: "The Messenger of Allah [SAW] said: 'Whoever changes his religion, kill him.'"
أَخْبَرَنَا الْحُسَيْنُ بْنُ عِيسَى، عَنْ عَبْدِ الصَّمَدِ، قَالَ حَدَّثَنَا هِشَامٌ، عَنْ قَتَادَةَ، عَنْ أَنَسٍ، أَنَّ ابْنَ عَبَّاسٍ، قَالَ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم " مَنْ بَدَّلَ دِينَهُ فَاقْتُلُوهُ " .
also referenced under: Hadith 4064 (Reference) & Book 37, Hadith 99 (In-Book)