Sunan Abi Dawud 4352
سنن أبي داود#4352SahihAbd Allah (b. Mas`ud) reported the Messenger of Allah (peace be upon him) as saying:The blood of a Muslim man who testifies that there is no god but Allah and that I am the Messenger of Allah should not be lawfully shed but only for one of three reasons: married fornicator, soul for soul, and one who deserts his religion separating himself from the community
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Al-AlbaniSahih
Muhammad Muhyi Al-Din Abdul HamidSahih
Shuaib Al ArnautSahih
Zubair Ali ZaiSahih Bukhari (6878) Sahih Muslim (1676)
In-book reference: 40:2