Musnad Ahmad 26:712

I read to my father: Ali ibn 'Asim narrated to you, he said: Ibrahim al-Hajari narrated to us, from Abu al-Ahwas, from Abdullah, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Insulting a Muslim is wickedness (fisq), and fighting him is disbelief (kufr), and the sanctity of his wealth is like the sanctity of his blood."