In this world,the sinner can be purified in one of three rivers:

  1.  A river of sincere repentance;
  2.   A river of good deeds that drowns the sins;
  3.    A river of calamities that wipe away his sins.

If these do not suffice in purifying him, then he will be purified in the river of Hell-fire in the hererafter.Therefore, when Allah intends good for his slave,He enters him into one of these three rivers, so he comes purified and cleansed on the Day of Judgement, not requiring the fourth purification. So swin in the river of repentance and doing good deeds, and have patience in the river of calamities. And  do not neglect these before a day comes when you will be drowned in the river of Hell-fire, whose fuel is men and stones.’ (Ibn al-Qayyin).