The fasting in the words of Imam As-Sadiq (peace be upon him)

All kinds of worship have a certain reward, and their blessings are connected to the life of the person either in this life or greater in the hereafter, such as the fasting that has a great reward as it has a great significance and importance when the person is really committed to it as it should be, as many of those who fast only get hunger and thirst. In fact the greatness of the month of Ramadan and the sanctity of its days urge us to prepare ourselves psychologically and socially.
From this standpoint Imam Ja'far As-Sadiq (peace be upon him) has explained what fasting really means:

“Fasting is not solely to abstain from eating and drinking. There are certain conditions to observe so that your fasting be valid. That is the inward fasting. Have you not heard what the daughter of Imran, Virgin Mary (peace be upon her) has said? “Surely I have vowed a fast to the Beneficent God, so I shall not speak to any human being today.” [It means ‘silence’].
Therefore, whenever you fast, keep your tongue from telling lies, lower your eyes (not to look lustfully at persons who it is unlawful to look at), do not quarrel with others, do not envy, do not dispute, do not challenge others, do not get angry, do not backbite, do not abuse anyone, do not talk badly, do not be lazy, do not bother others, do not oppress, do not be wasteful, do not torture anyone, and do not ignore the remembrance of God and prayer. Keep silent, be patient, be truthful, and wait for what God has promised you [the reappearance of the Imam of the time (may Allah hasten his reappearance)] while you are hopeful of meeting Him.
It is incumbent on you to be tranquil, humble, grave, and submissive as a servant afraid of his master, or like hopeful ones, who have purified their hearts from vices and observe openly and secretly what God has forbidden. Entrust yourselves completely to God while you are fasting. It is only then that you have observed fasting for the sake of God and have fulfilled your duties. If you fail to observe what has been ordained for you, it will be reduced from the reward of your fast.
The holy prophet (prayers and Allah's peace be upon him and his holy Household) heard a women curse her female slave. The messenger of Allah (prayers and Allah's peace be upon him and his holy Household) ordered food to be brought before the woman and asked her to eat. She said: “I am fasting, O messenger of Allah!” The holy prophet (prayers and Allah's peace be upon him and his holy Household) said: “How are you fasting while you are cursing your female slave? Surely, fasting does not just mean to abstain from eating or drinking. It means refraining from bad deeds and bad speech too. There are few people who are truly fasting but many who are hungry.”