Narrated Jabir bin 'Abdullah: When the Prophet called the people (Sadqa, a sub-narrator, said, 'Most probably that happened on the day of AlKhandaq) Az-Zubair responded to the call (i.e. to act as a reconnoiter). The Prophet) called the people again and Az- Zubair responded to the call. The Prophet then said, "Every prophet had a disciple and my disciple is Zubair bin Al- 'Awwam."

— Sahih Bukhari, Volume 4, Book 52: Fighting for the Cause of Allah (Jihaad), Hadith #100