Surah Al-Baqarah, Verse 239

فَإِنۡ خِفۡتُمۡ فَرِجَالًا أَوۡ رُكۡبَانٗاۖ فَإِذَآ أَمِنتُمۡ فَٱذۡكُرُواْ ٱللَّهَ كَمَا عَلَّمَكُم مَّا لَمۡ تَكُونُواْ تَعۡلَمُونَ٢٣٩

fa-in khif'tum farijālan aw ruk'bānan fa-idhā amintum fa-udh'kurū l-laha kamā ʿallamakum mā lam takūnū taʿlamūna

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.