Sunan Ibn Majah, Book 21, Hadith 2762 (In-Book) ⓘ
It was narrated from Ibn 'Abbas that the Prophet 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.”
حَدَّثَنَا مُحَمَّدُ بْنُ عَبْدِ الأَعْلَى الصَّنْعَانِيُّ، حَدَّثَنَا مُعْتَمِرُ بْنُ سُلَيْمَانَ، عَنْ أَبِيهِ، عَنْ حَنَشٍ، عَنْ عِكْرِمَةَ، عَنِ ابْنِ عَبَّاسٍ، عَنِ النَّبِيِّ صلى الله عليه وسلم قَالَ " لاَ يُقْتَلُ مُؤْمِنٌ بِكَافِرٍ وَلاَ ذُو عَهْدٍ فِي عَهْدِهِ " .
also referenced under: Hadith 2660 (Reference) & Volume 3, Book 21, Hadith 2660 (DarusSalam)