Muhammad bin Ja'far bin al-Zubair محمد بن جعفر بن الزبير بن العوام · Fasting (Kitab Al-Siyam)

A man came to the Prophet (ﷺ). He broke his fast during Ramadan. He then narrated the rest of this tradition adding: Then a huge basket containing fifteen sa's of dates was brought to him. He said: Eat it yourself and your family and keep one fast and beg pardon of Allah.

A man came to the Prophet (ﷺ) during Ramadan in the mosque. He said: Messenger of Allah, I am burnt. The Prophet (ﷺ) asked him what happened to him. He said: I had sexual intercourse with my wife. He said: Give sadaqah (alms). He said: I swear by Allah, I possess nothing with me, and I cannot do this. He said: Sit down. He sat down. While he was waiting, a man came forward driving his donkey loaded with food.…

If I had some part of the fast of Ramadan to make up, I would not be able to atone for it except in Sha'ban.