Fiqh-us-Sunnah Volume 1, Purification and Prayer, Fiqh 1.006B.

Najasah refers to impure substances that the Muslim must avoid and wash off if they should happen to contaminate his clothes, body and so on. Says Allah in the Qur’an, “Purify your raiment” (alMudathar 4); and, “Allah loves those who repent and who purify themselves” (al-Baqarah 222). The Messenger of Allah also said, “Purity is half of the faith.”