The Prophet ﷺ said, "Whoever kills a person under a covenant of protection from Allah and His Messenger will not catch the scent of Paradise, though its fragrance can be perceived from a distance of seventy years' travel."
حدثنا محمد بن بشار حدثنا معدي بن سليمان أنبأنا ابن عجلان عن أبيه
عن النبي ﷺ قال من قتل معاهدا له ذمة الله وذمة رسوله لم يرح رائحة الجنة وإن ريحها ليوجد من مسيرة سبعين عاما
Sourcing, [sahih] Tirmidhi narrated it in Diyat, the chapter on what has been said about one who kills a person under covenant of protection, hadith no. 1403, from Ibn Bashar with this wording, and he said, hasan sahih. Madi is daif, and Ibn Ajlan used ambiguous transmission (anana). It has preceded at hadith no. 1967, and the previous hadith serves as a corroborating witness for it.