Translation
(20) The Chapters on Legal Punishments
كتاب الحدود
(2) Chapter: The Apostates Who Leaves His Religion
(2.00) باب الْمُرْتَدِّ عَنْ دِينِهِ
Sunan Ibn Majah 2535 
It was narrated from Ibn`Abbas that the Messenger of Allah (ﷺ) said:
“Whoever changes his religion, execute him.”
حَدَّثَنَا مُحَمَّدُ بْنُ الصَّبَّاحِ، أَنْبَأَنَا سُفْيَانُ بْنُ عُيَيْنَةَ، عَنْ أَيُّوبَ، عَنْ عِكْرِمَةَ، عَنِ ابْنِ عَبَّاسٍ، قَالَ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم ‏(‏مَنْ بَدَّلَ دِينَهُ فَاقْتُلُوهُ ‏)‏‏.‏
Grade :  Sahih (Darussalam)
Reference : Sunan Ibn Majah 2535
In-book reference : Book 20, Hadith 3
English translation : Vol. 3, Book 20, Hadith 2535