Sunan At-Tirmidhi

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