Sahih Bukhari Volume 4, Book 56, Hadith 2848

حَدَّثَنَا صَدَقَةُ، أَخْبَرَنَا ابْنُ عُيَيْنَةَ، حَدَّثَنَا ابْنُ الْمُنْكَدِرِ، سَمِعَ جَابِرَ بْنَ عَبْدِ اللَّهِ ـ رضى الله عنهما ـ قَالَ نَدَبَ النَّبِيُّ صلى الله عليه وسلم النَّاسَ ـ قَالَ صَدَقَةُ أَظُنُّهُ ـ يَوْمَ الْخَنْدَقِ فَانْتَدَبَ الزُّبَيْرُ، ثُمَّ نَدَبَ فَانْتَدَبَ الزُّبَيْرُ، ثُمَّ نَدَبَ النَّاسَ فَانْتَدَبَ الزُّبَيْرُ فَقَالَ النَّبِيُّ صلى الله عليه وسلم ‏"‏ إِنَّ لِكُلِّ نَبِيٍّ حَوَارِيًّا، وَإِنَّ حَوَارِيَّ الزُّبَيْرُ بْنُ الْعَوَّامِ ‏"‏‏

Narrated By Jabir bin 'Abdullah : When the Prophet called the people (Sadqa, a sub-narrator, said, 'Most probably that happened on the day of Al-Khandaq) 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."