Musnad Ahmad 30:1277

Muhammad ibn Bishr narrated to us, Muhammad ibn ‘Amr narrated to us, Abu Salamah narrated to us, from Abu Hurairah, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "The Jews divided into seventy-one or seventy-two sects, and my nation will divide into seventy-three sects."