Sahih Muslim Book 31, Hadith Number 5938.
Chapter : The merits of Zubair and Talha (Allah be pleased with both of them).
Jabir b. Abdullah reported: I heard Allah’s Messenger (may peace be upon him) exhorting people on the Day of the Battle of the Ditch to fight. Zubair said: I am ready (to participate). He then again exhorted and he again said: I am ready to participate. Thereupon Allah’s Messenger (may peace be upon him) said: Behold. for every Prophet there is a helper and my helper is Zubair.