According to Sura XXV Furqan or The Criterion, Ayat 68 of Holy Quraan, there are three major sins which Allah will never forgive and their penalty will be doubled on the Day of Judgement. These are as follows:
1. False worship or Shirk which is a crime against God
2. Taking of innocent life, which is a crime against fellow-creatures
3.Fornication or Adultry, which is a crime against self respect