Nawawi Hadith #42: The Expanse of the Forgiveness of Allaah The Most High
(English Translation of the meaning)
On the authority of Anas (radiAllaahu anhu) who said:
I heard the Messenger of Allaah (sallAllaahu alayhi wa sallam) say:
Allaah the Almighty has said:
O Son of Aadam, as long as you invoke Me and ask of Me, I shall forgive you for what you have done, and I shall not mind. O Son of Aadam, were your sins to reach the clouds of the sky and you then asked forgiveness from Me, I would forgive you. O Son of Aadam, 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 [too].
(It was related by at-Tirmidhee, who said that it was a Hasan hadeeth.)