The reason this book opens with purification is that the authentic reports from the Prophet ﷺ outlining the rites of Islam begin with prayer, then zakat, then fasting, and then pilgrimage. In the ḥadith recorded by Imam Aḥmad (1009), Abū Dāwūd (61), al-Tirmidhī (2), and Ibn Mājah (275), the Prophet ﷺ said, “The key to prayer is purification.” A key must necessarily come before what it opens, so it is fitting to start with purification, for freedom from ritual impurity and physical filth is a prerequisite for prayer—and a prerequisite always precedes the act it conditions.

Al-Ghazālī said in Iḥyā’ ʿUlūm al-Dīn: Allah the Exalted says, “…to purify you thereby” (Al-Anfāl 8:11).

Muslim (223) also narrates from Abū Mālik al-Ashʿarī that the Messenger of Allah ﷺ said, “Purification is half of faith.”

Purification has four levels:

1. Cleansing the outward body from ritual impurities and physical defilements.
2. Cleansing the limbs from sins and transgressions.
3. Purifying the heart from blameworthy traits.
4. Purifying the innermost secret from anything other than Allah Most High.

This represents the ultimate goal for one whose inner sight is strong enough to aspire to it; but whoever is blind of heart understands nothing of purification beyond the first level.

By default, purification is carried out with water, for water is the best of solvents—every substance dissolves in it. Its cleansing power lies in its remaining in its original, natural state; when something mixes with it and changes its very name, its capacity to remove impurities and to purify is weakened, for it then loses its lightness, delicacy, flow, and penetrating ability.