Musnad Ahmad 5:237

'Affan narrated to us, Hammad narrated to us, 'Asim ibn Bahdalah informed us, from Zirr ibn Hubaysh, that it was said to 'Ali: "The killer of Az-Zubayr is at the door." He said: "Let the killer of the son of Safiyyah enter the Fire. I heard the Messenger of Allah, peace and blessings of Allah be upon him, say: 'Indeed, every prophet has a disciple (hawari), and Az-Zubayr is my disciple.'"