Musnad Ahmad 284:15

Yunus narrated to us, he said: Hammad—meaning Ibn Zayd—narrated to us, from Hisham ibn Urwah, from his father, from Abdullah ibn al-Zubayr, that the Prophet, peace and blessings of Allah be upon him, said: "For every prophet there is a disciple (hawari), and al-Zubayr is my disciple, and the son of my paternal aunt."