The Messenger of Allah ﷺ said, "A Muslim is not to be killed in retaliation for a disbeliever." He also said, "The blood-money for a disbeliever is half the blood-money of a believer."
أن رسول الله ﷺ قال: لا يقتل مسلم بكافر، وقال: دية عقل الكافر نصف دية عقل المؤمن.
Tirmidhi (1413) narrated it, and this is his wording, as did Ahmad (6692) and others, through various chains from Amr bin Shuayb, from his father, from his grandfather, who related it. Its chain is hasan because of Amr bin Shuayb. It is part of the Prophet's ﷺ sermon at the conquest of Makkah, and it is given in full in the account of the conquest of Makkah.Similar in meaning is what was narrated from Ibn Umar in a long hadith, "A believer is not killed for a disbeliever, nor is one bound by a covenant killed while his covenant stands." Ibn Hibban (5996) narrated it through Qasim bin Walid, from Sinan bin Harith bin Musrif, from Talha bin Musarrif, from Mujahid, from Ibn Umar, who related it.Ibn Hibban mentioned this Sinan in Thiqat (6/424) and did not mention any narrator from him other than Qasim bin Walid. Abu Hatim added Muhammad bin Talha, and Abu Hatim's son added "Salih bin Huyayy, the father of Hasan bin Salih." But no one besides Ibn Hibban regarded him as reliable, so according to Ibn Hajar's view he is "acceptable," that is, when corroborated by others.