It was narrated from Ibn 'Abbas that the Prophet (ﷺ) said:
"A believer should not be killed in retaliation for the murder of a disbeliever, and a person who has a treaty should not be killed during the time of the treaty." (FR)
English reference (FR): Vol. 3, Book 21, Hadith 2660 (FR)
Arabic reference (FR): Book 21, Hadith 2762 (FR)