What is upon a person who breaks his fast in the month of Ramadan purposely out of choice and he is person who is supposed to fast?
Shaykh ‘Ubayd al-Jaabiri said:
The answer to that is first and foremost, he must repent to Allah and seek forgiveness from Allah for he has committed an evil sin by breaking his fast without a particular excuse for breaking that fast.
Secondly, the fast of that day is void, so he has to fulfil that day on another day, in another time.
And if somebody says how can we understand the hadeeth that whoever breaks his fast in the days of Ramadan then even if he were to fast the whole of his life he would not be able to bring that day?
That Hadeeth is weak because there is a narrator who is unknown in the chain of narration and the shaykh says that I think his name is either Abu Muthawis or ibnu Muthawis.
And thirdly, the person must stop the sin and continue to fast for the rest of that day. He is not allowed to continue eating or drinking or to continue having relations.