An-Nisa' (The Women)
Surah 4 · Verse 101
And when you go striking in the earth, then there is no sin on you if you shorten (something) from the worship (salat), if you fear that those who do not believe will persecute you. The infidels are certainly your n enemies.
Shortening of Salat is permitted during battles, wars etc. due to the fear of persecution by the opponents, but as soon as there is safety, regular Salat is to offered at fixed times.
