Islamic Prayer of Repentance

Say, O My slaves who have been prodigal to their own hurt! Despair not of the mercy of God, who forgives all sins. Lo! He is the Forgiving, the Merciful. Turn to Him repentant, and surrender unto Him, before there can come upon you the doom, when you cannot be helped. And follow the better of that which has been revealed unto you from your Lord, before the doom comes on you suddenly when you know not. Lest any soul should say, "Alas, my grief that I was unmindful of God, and I was indeed among the scoffers!" Or should say, "If God had but guided me, I should have been among the dutiful!" Or should say, when it sees the doom, "Oh, that I had but a second chance, that I might be among the righteous!"

Source: Islam. Qur'an 39.53-58