Surah Al-Baqarah, ayah 239

2:239

فَإِنۡ خِفۡتُمۡ فَرِجَالًا أَوۡ رُكۡبَانٗاۖ فَإِذَآ أَمِنتُمۡ فَٱذۡكُرُواْ ٱللَّهَ كَمَا عَلَّمَكُم مَّا لَمۡ تَكُونُواْ تَعۡلَمُونَ ٢٣٩

Fa in khiftum farijālan aw rukbānan fa idhā amintum fadhkurullāha kamā 'allamakum mā lam takūnū ta'lamūn

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.