Ibn ʿUmar said something similar to Mujahid's saying: Whenever (Muslims and non-Muslims) stand face to face in battle, the Muslims can pray while standing. Ibn ʿUmar added, "The Prophet ﷺ said, 'If the number of the enemy is greater than the Muslims, they can pray while standing or riding (individually).' "  

عَنِ النَّبِيِّ ﷺ وَإِنْ كَانُوا أَكْثَرَ مِنْ ذَلِكَ فَلْيُصَلُّوا قِيَامًا وَرُكْبَانًا