Musnad Ahmad 27:1239

'Uthman ibn 'Umar narrated to us, Malik ibn Mighwal informed us, from Junayd, from Ibn 'Umar, that he heard the Prophet, may Allah bless him and grant him peace, say: "Hell has seven gates; one of them is for the one who draws his sword against my Ummah," or he said, "the Ummah of Muhammad."