Musnad Ahmad 1018:67

Muhammad ibn Ja'far narrated to us, Shu'bah narrated to us, from Mansur, from Hilal ibn Yasaf, from al-Qasim ibn Mukhaymirah, from a man among the companions of the Prophet, may Allah bless him and grant him peace, from the Prophet, may Allah bless him and grant him peace, that he said: "Whoever kills a man from the people of the covenant (ahl al-dhimmah) will not smell the fragrance of Paradise, or will not find the scent of Paradise." Mansur is the one who expressed doubt, [adding]: "Indeed, its scent is found from a distance of seventy years."