Can the reconnoitrer be sent alone?
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 Jabir bin `Abdullah: When the Prophet (ﷺ) called the people (Sadqa, a sub-narrator, said, 'Most likely that happened on the day of Al-Khandaq) Az-Zubair responded to the call (i.e. to act as a scout). The Prophet) called the people again and Az-Zubair responded to the call. The Prophet (ﷺ) then said, "Every prophet had a disciple and my disciple is Zubair bin Al-`Awwam."