The Treatise on Rights by Imam Zain al Abidin (A.S) -11

11. Rights of Fasting

"The right of fasting is that you know it is a veil which Allah has set up over your tongue, your hearing, your sight, your stomach, and your private part to protect you from the Fire. If you abandon the fast, you will have torn Allah's protective covering away from yourself. There is no strength save in Allah." 

As for fasting, it is among the most important beliefs in Islam. It has been mentioned in the tradition that it is protection from the Fire. Many psychological, moral, economic, social, and health profits result from it. Among them is that it strengthens the activity of will through which man achieves his important objectives in life. The Muslim researchers have mentioned the profits which result from fasting and written books about them. 

Any how, in his words, the Ima`m has mentioned what the fasting should do during their fast. He has mentioned that they should not confine their fasting to refraining from food and drink; rather they should withhold their tongues from telling lies and falsehood, their ears from backbiting, their private parts from the unlawful, and their stomachs from the forbidden, that they may save themselves from Allah's chastisement and punishment.