Mukhtasar Sahih Bukhari — Hadith 1341

Narrated by Sayyiduna Abdullah bin Amr (may Allah be pleased with them both) from the Messenger of Allah (peace and blessings be upon him) that he said: "Whoever kills a dhimmi (non-Muslim under Muslim protection) unjustly will not even smell the fragrance of Paradise, and indeed, the fragrance of Paradise is perceived from a distance of forty years."