Successful indeed are the believers
Those who humble themselves in their prayers;
And who keep aloof from what is vain,
Who are active in deeds of charity;
Who abstain from sex, except from their wives or those whom their right hands possess, for they surely are not blameable, but those whose desires exceed those limits are transgressors;
Those who faithfully observe their trusts and their covenants;
And who (strictly) guard their prayers;
These are the heirs who will inherit Paradise: they will dwell therein (for ever). [Qur’an 23:1-11]
When we voluntarily restrict our desires and appetites, and refrain our impulse to overindulge, we are practicing abstinence. Historically, abstinence was associated with moral and spiritual considerations. Often, religious doctrine encouraged and defined the practices.
Christianity, to some extent, redefined abstention by incorporating unique monastic and ascetic practices into its orthodoxy. Passionate devotees often adopted mortification of the flesh as a substitute for martyrdom. Hermits, cenobites, desert anchorites, stylites, discalced and cloistered nuns and penitent monks highlighted the early period of Christian expansion. Their abstention and self-mortification testified to their faith and generated great respect and reverence.
Indeed, it would be difficult to point out a single great champion of Christian civilization who was not trained to the spiritual combat in the wilderness. [Catholic Encyclopedia]
For several generations, abstinence referred primarily to drinking alcohol, with temperance and sobriety the goals. More recently, discussions on abstinence often focused on sexual activity. Today, however, abstinence is usually associated with dietary and therapeutic practices somewhat distant from morality and religion.
We should, obviously, abstain from activities detrimental to us (e.g., drug abuse, smoking), yet difficult to abandon. Greed and promiscuity are also excellent targets for abstention. Likewise, cheating, lying, backbiting and similar human deficiencies that are inherently destructive can be tamed, if not eliminated, by consciously restricting them for periods. By abstaining from them, we train ourselves to root them out completely.
Refrain tonight, And that shall lend a kind of easiness To the next abstinence: the next more easy; For use almost can change the stamp of nature, And either master the devil or throw him out with wonderous potency . [William Shakespeare Hamlet, III.4]
Abstention may also include refraining from beneficial and wholesome activities such as sleeping, speaking, marital sex and eating certain foods. We may do so as an act of penance, to show regret for a sin or crime, to satisfy a vow, or to protest or demonstrate against a grievance.
Exhortations to fasting are frequently accompanied by reminders to abstain from conduct condemned by God, and by encouragement to righteousness and good deeds. Merely leaving food for a few hours while continuing to indulge in spiritually harmful activities is wasted effort.
Prophet Muhammad (PBUH) is reported to have said:
Fasting is a shield. When any one of you is fasting on a day, he should neither indulge in obscene language, nor raise the voice; or if anyone reviles him or tries to quarrel with him he should say: I am a person fasting. [Sahih Muslim, Book 006, Number 2566]
Allah is not in need of anyone abandoning his food and drink who does not abandon lies and acting by them while fasting. [The Sahih Collection of al-Bukhari, by Imam Bukhari, Chapter 35. Book of Fasting VIII:1804.
St. John Chrysostom defines fasting in terms of abstaining from sin, not from food:
I speak not, indeed, of such a fast as most persons keep, but of real fasting; not merely an abstinence from meats; but from sins too. For the nature of a fast is such, that it does not suffice to deliver those who practice it, unless it be done according to a suitable law.
I have said these things, not that we may disparage fasting, but that we may honour fasting; for the honour of fasting consists not in abstinence from food, but in withdrawing from sinful practices; since he who limits his fasting only to an abstinence from meats, is one who especially disparages it. Dost thou fast? Give me proof of it by thy works! Is it said by what kind of works? If thou seest a poor man, take pity on him! If thou seest an enemy, be reconciled to him! If thou seest a friend gaining honour, envy him not! If thou seest a handsome woman, pass her by!
For let not the mouth only fast, but also the eye, and ear, and the feet, and the hands, and all the members of our bodies. Let the hands fast, by being pure from rapine and avarice. Let the feet fast, but ceasing from running to the unlawful spectacles. Let the eyes fast, being taught never to fix themselves rudely upon handsome countenances, or to busy themselves with strange beauties. For looking is the food of the eyes, but if this be such as is unlawful or forbidden, it mars the fast; and upsets the whole safety of the soul; but if it be lawful and safe, it adorns fasting. For it would be among things the most absurd to abstain from lawful food because of the fast, but with the eyes to touch even what is forbidden. Dost thou not eat flesh? Feed not upon lasciviousness by means of the eyes. Let the ear fast also. The fasting of the ear consists in refusing to receive evil speakings and calumnies. "Thou shalt not receive a false report," it says. [St. Chrysostom: On the Priesthood; Ascetic Treatises; Select Homilies and Letters; Homilies on the Statutes, Homily III, 8,11]