Musnad Ahmad 1660

An-Nadr bin Shaiban said: I met Abu Salamah bin ‘Abdur Rahman and said: Tell me of something you heard from your father, that he heard from the Messenger of Allah (ﷺ) about the month of Ramadan. He said: Yes; my father told me that the Messenger of Allah (ﷺ) said: “Allah, may He be glorified and exalted, enjoined fasting Ramadan and l have made it Sunnah to pray qiyam during it [i.e., Taraweeh]. Whoever fasts it and prays qiyam during it, out of faith and seeking reward, will emerge from sins as on the day his mother bore him.”