Sheikh Yusuf Al-Qaradawi, the prominent Muslim scholar, states: Actually, man is held accountable for each of his deeds separately. So, what you should actually ask about is not whether he is to be rewarded for the days he fasted, but rather whether he can later make up for the fast-days he deliberately broke.
It is generally known that no days are equivalent to the days of Ramadan except the days of another Ramadan. At the same time, all days of Ramadan are originally fast-days, so that one can never make up for the missed fast-days of Ramadan during another Ramadan. That is why Abu Hurairah, may Allah be pleased with him, said: “Whoever did not observe fast for one day of Ramadan for no legal excuse or on account of a disease can never make it up later.” (Narrated on the authority of Abu Hurairah, by Al-Tirmidhi, Abu Dawud, An- Nasa’i, Ibn Majah, Ibn Khuzaimah, and Al-Bayhaqi, and the quoted version is At-Tirmidhi’s.) However, one of its narrators is weak.
It was also narrated, on the authority of Abu Hurairah, that a man did not observe fast in Ramadan deliberately with no legal excuses. Hence, Abu Hurairah said: “Even if he fasts for a whole year, he will still not have made up for that day.” It was also narrated, on the authority of Ibn Masu`d, that the Prophet, peace and blessings be upon him, said: “If anyone breaks his fast one day in Ramadan without a concession granted to him by Allah, a perpetual fast will not atone for it.” “Whoever breaks his or her fast for one day of Ramadan deliberately without any legal concession, then even if he observed fast for life, it would not compensate for that day.” Abu Bakr and `Ali Ibn Abi Talib were also reported to have said words with the same meaning.
Therefore, a Muslim must fear Allah and keep from deviating from the right path by observing the fast of Ramadan. He must have the ability to resist his desires, for whoever is defeated by hunger can never be victorious.