And if you fear [an enemy, then pray] on foot or riding. (2:239)

﴿فَإِنْ خِفْتُمْ فَرِجَالًا أَوْ رُكْبَانًا ۖ فَإِذَا أَمِنتُمْ فَاذْكُرُوا اللَّهَ كَمَا عَلَّمَكُم مَّا لَمْ تَكُونُوا تَعْلَمُونَ﴾
[ البقرة: 239]

2:239 And if you fear [an enemy, then pray] on foot or riding. But when you are secure, then remember Allah [in prayer], as He has taught you that which you did not [previously] know.

If you face danger from an enemy or any other danger, and you are not able to offer the prayer completely, then pray whilst walking or riding, on camels, horses, or in any way you can.
If the danger has gone, remember Allah as He has taught you: remembering Him in the most complete manner within the prayer.
Also, remember Him for His having taught you guidance and given you light which you were previously unaware of.

And if you fear (an enemy), perfrom Salat (pray) on foot or riding. And when you are in safety, offer the Salat (prayer) in the manner He has taught you, which you knew not (before).

phonetic Transliteration

Fain khiftum farijalan aw rukbanan faitha amintum faothkuroo Allaha kama AAallamakum ma lam takoonoo taAAlamoona

Abdullah Yusuf Ali - Translation

If ye fear (an enemy), pray on foot, or riding, (as may be most convenient), but when ye are in security, celebrate Allah's praises in the manner He has taught you, which ye knew not (before).

Safi-ur-Rahman al-Mubarakpuri

And if you fear (an enemy), (perform Salah) on foot or riding. And when you are in safety, then remember Allah (pray) in the manner He has taught you, which you knew not (before).

Page 39 English transliteration