From Sahih Bukhari (Hadith 2997):
Narrated Jabir bin `Abdullah:On the day of the battle of the Trench, the Prophet (ﷺ) wanted somebody from amongst the people to volunteer to be a reconnoitre. Az-Zubair volunteered. He demanded the same again and Az-Zubair volunteered again. Then he repeated the same demand (thrice) and Az-Zubair volunteered once more. The Prophet (ﷺ) then said, " Every prophet has a disciple and my disciple is Az-Zubair
Reference: Bukhari 2997