Sahih Muslim Book 37, Hadith Number 6668.
Chapter : Throwing of non-believers in hell-fire for believers as Divine Grace and Mercy.
Abu Burda reported Allah’s Messenger (may peace be upon him) as saying: There would come people amongst the Muslims on the Day of Resurrection with as heavy sins as a mountain, and Allah would forgive them and He would place in their stead the Jews and the Christians. (As far as I think), Abu Raub said: I do not know as to who is in doubt. Abu Burda said: I narrated it to ‘Umar b. ‘Abd al-‘Aziz, whereupon he said: Was it your father who narrated it to you from Allah’s Apostle (may peace be upon him)? I said: Yes.