“Struggle against your soul with the swords of self-discipline. They are of four kinds: little nourishment, sleeping little, speaking only when there’s a need and bearing wrongs enacted against you. Restricting your eating will be the death of unwanted passions; sleeping little clarifies ones aspirations; speaking little keeps one safe from afflictions and bearing injustices against oneself will help you obtain your goals, for there is nothing more arduous against God’s servant than to grant clemency when one is repudiated, bearing wrongs inflicted on oneself by others.
And when your passions begin to stir your soul to unwanted ends and sins, and one feels delight in indulgence, unsheathe the sword of eating little from the scabbard Tahajjud and sleep but little. Strike these desires with the fists of lethargy and silence until they no longer oppress you nor avenge themselves against you and you are safe from their calamities til the end of your days, having purified them of the darkness of carnal desires, so that you escape unscathed from their perilous consequences. From this point you will become pure, immaculate and radiant, subtle in spirituality, free to roam about all that is good, traversing the paths of obedience to God like a fleet-footed steed in the field, like a king promenading in his garden.”
– Imam al-Ghazali on Disciplining the Soul