(And when ye go forth in the land) when you travel, (it is no sin for you to curtail (your) worship) curtail the prayer that a sedentary Muslim would usually perform (if ye fear) if you know (that those who disbelieve may attack you) may kill you while in prayer. (In truth the disbelievers are an open enemy to you) this is what is called the prayer of fear (salat al-khawf).