It is also important to emphasize that we must be extra careful and refrain from all sin during the fasting month. As we are in a season of worship, then committing a sin becomes increasingly obnoxious. The Prophet (peace be upon him) makes clear that doing what is forbidden does not fit with fasting. Abu Hurayrah quotes him as saying: Whoever does not refrain from falsehood, whether verbal or practical, should know that God has no need for him to abstain from food and drink. (Related by Al-Bukhari).
In the Arabic text, the word the Prophet uses for falsehood' is zoor, which signifies a false statement, perjury and deliberate lying. However, the Prophet adds any practical action based on it. Scholars explain that what is meant here is all forbidden things, whether verbal or practical. The Hadith is thus taken to warn against all sinful action. It may be understood to mean that a person who does not abandon falsehood of all types, at all times, will benefit nothing by fasting. It may also mean that a person who does not abandon sin during fasting renders his fasting without reward.
What does the Prophet mean when he says that God has no need for such person's fast? Certainly God needs nothing from us. We are the ones who need our worship, as it refines our sense of goodness and strengthens our will to do only what is good. Worship certainly makes us better people. We also need it to earn God's reward. The Prophet is saying here that indulging in falsehood, of any type, renders our good actions worthless. In other words, sinful action outweighs good deeds and makes them earn no reward. In another Hadith, the Prophet asked his companions: Do you know who is bankrupt? They said: A bankrupt person is one who has neither money nor possessions. He said: No. He is one who gets to the Day of Judgement having done his prayers, fasting and zakat, but has also abused this person and beaten up that person. He has to compensate them, giving them some of his good deeds. When he no longer has any, he is made to take over some of their sins. He ends up in hell.
This is a graphic definition of a person whose good actions are outweighed by his ill conduct. It shows that good action must be accompanied by refraining from bad one, so that it earns good reward. The same import is highlighted in the Hadith about the need to abstain from all falsehood when fasting.
Two questions need to be answered here: 1) Does sin render fasting invalid? and 2) Should a person who commits falsehood discontinue his fast?
To answer the first question we may say that Imam Al-Ghazali considers that lying and backbiting render fasting invalid. Imam Ibn Hazm goes further and says that a person who deliberately commits any sin, while mindful that he is fasting, renders his fast invalid. The majority of scholars, however, say that fasting remains acceptable, but the one who commits such a sin must repent and seek forgiveness. This gives us the answer to the second question. He must not discontinue his fast. If he does, he aggravates his position by committing another sin, which is not fasting. However, he must be genuinely sorry for having committed a sin, declare his repentance and pray God to forgive him. If the sin committed is against another person, he should make it up with that person.