3.157 – If indeed you are killed in the way of God, or die – forgiveness from God
The idea that believers who die fighting are martyrs who go straight to heaven has its quranic basis in verses like this, one of three such passages in this sūra. Here fighters are promised forgiveness, mercy, and being gathered to Allah (v. 158). Other verses like this are 2.154; 3.169–72, 195; 22.58–59; and 47.4–6. See an analysis of these verses at 47.4.