I heard the Prophet ﷺ say, "When a slave flees to the land of polytheism, his blood becomes lawful."
حدثنا قتيبة بن سعيد حدثنا حميد بن عبد الرحمن عن أبيه عن أبي إسحق عن الشعبي
سمعت النبي ﷺ يقول إذا أبق العبد إلى الشرك فقد حل دمه
Sourcing, [sahih] Nasai narrated it in Tahrim al-Dam, chapter on the slave who flees to the land of shirk, etc., no. 4057, from Qutayba with this wording, and Muslim narrated it, no. 70, through another route from Shaybi with this wording.