The Prophet ﷺ said, "Whoever fasts Ramadan out of faith and in hope of reward will be forgiven his past sins, and whoever spends Laylat al-Qadr in prayer out of faith and in hope of reward will be forgiven his past sins."
حدثنا عبد الصمد وأبو عامر قالا حدثنا هشام فذكرا مثله إلا أنهما قالا من قام رمضان إيمانا
Its chain of transmission is sahih.