Anas ibn Mālik (may Allah be pleased with him) reported: I heard the Messenger of Allah (may Allah's peace and blessings be upon him) saying: "Allah, the Exalted, said: 'O son of Adam, so long as you call upon Me and ask of Me, I shall forgive you for what you have done, and I shall not mind. O son of Adam, were your sins to reach the clouds of the sky and were you then to ask forgiveness of Me, I shall forgive you. O son of Adam, were you to come to Me with sins nearly as great as the earth and were you then to meet Me, ascribing no partner to Me, I shall bring you forgiveness nearly as great as it.'"
Explanation:
This Hadīth indicates the vastness of Allah's mercy and generosity. It clarifies the means to attain His forgiveness, which are supplication and asking Him for forgiveness. These two means are contingent upon monotheism. So whoever dies believing in Allah as the only deity worthy of worship, his supplication and seeking forgiveness will avail him. Meanwhile, polytheism renders all deeds futile. Nothing avails a person who dies upon polytheism; neither supplication nor any other deed.