Fiqh-us-Sunnah Volume 3, Zakaat and Fasting, Fiqh 3.132A.

Fasting is a type of worship that draws one closer to Allah. Allah has prescribed it to purify the soul and to train it in good deeds. The fasting person must be on guard against any act that may cause him to lose the benefits of his fast. Thus, his fast will increase his God-consciousness, and Allah says in the Qur’an: “O you who believe, fasting is prescribed for you as it was prescribed for those before you so perchance you may attain God consciousness.”

Fasting is not just refraining from eating and drinking, but it is also refraining from everything else that Allah has forbidden. Abu Hurairah reported that the Prophet said: “Fasting is not [abstaining] from eating and drinking only, but also from vain speech and foul language. If one of you is being cursed or annoyed, he should say: “I am fasting, I am fasting.” This is related by Ibn Khuzaimah, Ibn Hibban, and al-Hakim. The latter said that it is sahih according to Muslim’s criterion.

Abu Hurairah also reported that the Prophet, upon whom be peace, said: “Allah does not need the fast of one who does not abandon false speech or acting according to his false speech.” This is related by the group, except for Muslim.

Abu Hurairah narrated that the Prophet said: “Perhaps a fasting person will get nothing from his fast save hunger, and perhaps the one who stands to pray at night will get nothing from his standing except sleeplessness.” This is related by an-Nasa’i, Ibn Majah, and al-Hakim. The latter said that it is sahih according to alBukhari’s criterion.