Abu Huraira reported Allah’s Messenger (may peace be upon him) as saying: He who observed prayer at night during Ramadan, because of faith and seeking his reward from Allah, his previous sins would be…

Abu Huraira reported Allah’s Messenger (may peace be upon him) as saying: He who observed prayer at night during Ramadan, because of faith and seeking his reward from Allah, his previous sins would be forgiven.
Source: HOTD