Al-Baqara 2:239

If you are in danger[133], then pray while walking or riding. But when you are safe, remember Allah as He taught you what you did not know.

[133] Of an imminent danger such as enemies and the like.

And if you fear [an enemy, then pray] on foot or riding. But when you are secure, then remember Allāh [in prayer], as He has taught you that which you did not [previously] know.

239. And if you fear (an enemy), perform Salât (pray) on foot or riding.[63] And when you are in safety, offer the Salât (prayer) in the manner He has taught you, which you knew not (before).

[63] (V.2:239) Narrated Sâlih Khawwat or Sahl bin Abî Hathmah concerning those who witnessed the Fear Prayer that was performed in the battle of Dhat-ur-Riqa‘ in the company of Allâh’s Messenger صلى الله عليه وسلم: One batch lined up behind him while another batch (lined up) facing the enemy. The Prophet صلى الله عليه وسلم led the batch that was with him in one Rak‘ah, and he stayed in the standing posture while that batch completed their (two Rak‘at) prayer by themselves and went away, lining in the face of the enemy, while the other batch came and he (i.e. the Prophet صلى الله عليه وسلم) offered his remaining Rak‘ah with them, and then, kept on sitting till they completed their prayer by themselves, and he then finished his prayer with Taslîm along with them. [Sahih Al-Bukhâri, Vol. 5, Hadîth No.451].

And if ye go in fear, then (pray) standing or on horseback. And when ye are again in safety, remember Allah, as He hath taught you that which (heretofore) ye knew not.