Taharat-e-Batini or inward purity can be achieved through a clean and pure thinking process, by avoiding evil thoughts.
One of my favorite hadiths or Prophetic anecdotes teaches: “Purity is half of faith, prayer is a light, charity is proof, and patience is illumination”.
In this Prophetic tradition, the Arabic word meaning ‘purity’ is “Taharat” which encompasses two spiritual dimensions: (1) taharat-e-batini, inward purity and (2) taharat-e-zahiri, outward purity.
Taharat-e-Batini or inward purity can be achieved through a clean and pure thinking process, by avoiding evil thoughts and engaging in constant spiritual meditation (dikr). It directly helps the heart and mind to be pure and sound, purging them of spiritual maladies such as anger, hatred, jealousy, egoism etc. However, Taharat-e-Zahiri or outward purity is attained by properly maintaining the physical cleanliness—for instance, making wudu (ablution), taking shower (ghusl), using fragrance or perfumes (itar) and keeping house and clothes neat and clean.
One of the earliest Sufis in India, Hazrat Data Ganj Baksh Hijweri states in his mulfuzat (Sufi discourses): “After iman (faith in God), the most imperative link of the Sufi life style is Taharat which includes both kinds of cleanliness: purity of body and mind. Just as prayer or devotion cannot be accepted without Taharat-e-Zahiri, similarly wisdom or ma’arifat cannot be attained without Taharat-e-Batini. The latter is also known as tazkiyah (purification of soul). In fact, the practice of Sufism or tasawwuf is nothing but tazkiyah.
Tazkiyah empowers one to curb all the demonic forces (quwwah-e-wahmiyya), ferocious thoughts (quwwa-e-ghazabiyya) and animalistic impulses (quwwah-e-shahwania). Therefore, Prophets, their close companions (Sahaba) and Sufis used to profess and practice the tazkiyah. They would often exhort: “purify yourself, you will have no disease”. Thus, they alluded to various forms of disease that emanate from moral and spiritual maladies.
A Naqshbandi Sufi saint writes that Tazkiyah is the essential Islamic teaching upon which all Sufi teachings are primarily based. In the Sufi view, the purification (Tazkiyah) of Nafs (spirit) requires the purity of all faculties of the soul including Qalb (heart), Ruh (spirit) and Aql (mind). Thus, Purification of the soul or Tazkiyah-e-Nafs requires one to eschew all baser instincts that prevent a person from developing into a divine existence. Not only major sins like hatred, lying, slandering, but what is seen as minor evils such as backbiting, jealousy, envy, greed etc. are also completely annihilated in the process of Tazkiyah.
One who treads the path of Tazkiyah must be cognizant enough of all this. S/he should constantly engage in self-evaluation in terms of the actions s/he has done. An honest introspection is required to ascertain that mind and heart are purged of all evil impulses of Nafs, one by one, and thus determine the purity of the soul (Tazkiyah). This is the broader meaning of the Prophetic saying: “Purity is half of the faith”. Qur’an has also explained it in this verse: “And by the Soul (Nafs), and the One Who perfected man in proportion; indeed, whoever purifies his own soul, succeeds and indeed, whoever corrupts his own soul, fails.” (91:9-10).