The Muslims are unanimously agreed on the obligation of fasting Ramadan, and whoever denies it is deemed an unbeliever.

The wisdom behind legislating the fast is that it purifies and refines the soul, cleansing it of harmful humors and ignoble traits. It narrows the channels through which Satan moves within the human body—for Satan flows through the son of Adam as blood flows. When a person eats or drinks, his lower self expands toward its desires, his willpower weakens, and his appetite for acts of worship diminishes, whereas fasting produces the opposite effect.

Fasting also detaches the heart from worldly pleasures, turns one’s aspiration toward the Hereafter, and stirs compassion for the needy, because the fasting person tastes the pain of hunger and thirst. In the Sacred Law, fasting is the deliberate abstention from specific matters—eating, drinking, sexual intercourse, and whatever else the Law has named—and this abstention is accompanied by refraining from obscene speech and sin.

The daily fast becomes obligatory at the appearance of the second dawn—the horizontal whiteness that spreads across the horizon—and ends at sunset. The Almighty says: “So now lie with them (i.e., your wives) and seek what Allah has decreed for you. Eat and drink until the white thread of dawn becomes distinct to you from the black thread; then complete the fast until nightfall” (Q 2:187). The phrase “until the white thread of dawn becomes distinct from the black thread” means that the whiteness of daytime is clearly separated from the darkness of night.

The obligation to fast the month of Ramadan begins once its arrival is established. There are three ways to ascertain its commencement: