´Narrated Abu Hurairah:` that the Prophet (ﷺ) said: "Indeed, whoever kills a Mu'ahid that has a covenant from Allah and a covenant from His Messenger (ﷺ), then he has violated the covenant with Allah and the covenant of His Messenger, so he shall not smell the fragrance of Paradise; even though its fragrance can be sensed from the distance of seventy autumns."
Hadith Referenceسنن ترمذي / كتاب الديات عن رسول الله صلى الله عليه وسلم / 1403