Quran 2:238-239:
[This is the sharī‘ah of God. If you want to remain steadfast on it,] be watchful over your prayers, [624] especially the one which comes in the middle [625] [of the morning and evening prayers when it is not easy for you to take out time from your involvements], and stand before God devoutly [leaving aside everything].Then if you fear any danger, pray on foot or while riding, in whichever way you like, but when circumstances become secure, remember [626] God in the very manner [627] He has taught you, which you knew not.
Translation by Javed Ahmed Ghamidi
English rendition by Dr. Shehzad Saleem