There was a young man among the children of Israel who worshipped Allah SWT (God) for twenty years. He then disobeyed Allah for twenty years. Then, one day, looking in the mirror, he noticed the whiteness of his beard and was taken aback by what he saw.

He said, "O my Lord, I had obeyed you for twenty years and I then disobeyed you for twenty years. Now if I return to You, will You accept me?"

He then heard a caller say, "You loved Us and We loved You. You left Us, and so We left you. You disobeyed Us, and so We gave you respite. And if you return to Us, We will accept you."

Allah SWT (God) says to the believers in a Hadith Qudsi:

"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 would 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 face Me, ascribing no partner to Me, I would bring you forgiveness nearly as great as it." (Sahih Bukhari Muslim).