narration found in regards to fasting and expiation (otherwise known as kaffarah).

Before going on to discuss this, let us briefly discuss a general ruling regarding fasts becoming invalid: if a sane, adult and resident (not travelling) Muslim fasts for Ramadan, but deliberately engages in sexual intercourse or consumes something to enjoy its taste, without anything compelling him to do so, his fast shall become invalid. Both expiation and making up the missed fast are mandatory for him.^[1]

To make up this missed fast, a person should keep another fast in a time other than Ramadan. In terms of expiation, a person must free a male or female slave if possible. If this is not found to be possible, he will have to fast 60 days consecutively. If this is not possible either, he will have to feed two meals to 60 poor people to their fill at two mealtimes.^[2]

This law applies to every Muslim whose fasts become invalid in this way, but the lawgiver of Islam, the best of creation, the final Prophet of Allah صَلَّى الـلّٰـهُ عَلَيْهِ وَاٰلِهٖ وَسَلَّم exempted a blessed Companion from this compensation in an extremely beautiful way.

When penalty became reward

As narrated by Abu Hurayrah رَضِىَ الـلّٰـهُ عَـنْهُ :

A person came and lamented, “O Messenger of Allah صَلَّى الـلّٰـهُ عَلَيْهِ وَاٰلِهٖ وَسَلَّم ! I have been destroyed!”

“What has brought about your destruction?”, the Messenger of Allah صَلَّى الـلّٰـهُ عَلَيْهِ وَاٰلِهٖ وَسَلَّم enquired. 

He replied: “I had intercourse with my wife during (the fast of) Ramadan.”