Musnad Ahmad 1688

It was narrated from Nadr bin Shaiban al-Huddani that Abu Salamah bin "Abdur-Rahman said: I said to him: Why don"t you tell me a hadeeth from your father that your father heard from the Messenger of Allah (ﷺ)? He said: Ramadan came and the Messenger of Allah (ﷺ) said: "Ramadan is a month that Allah has enjoined fasting and I have established the Sunnah of praying qiyam during it for the Muslims. Whoever fasts it out of faith and seeking reward will emerge from his sins as on the day his mother bore him.”