Fiqh-us-Sunnah Volume 3, Zakaat and Fasting, Fiqh 3.002.

Section : Exhortation to Give Zakah in the Qur’an.

At-Taubah 103 authorizes the Prophet, upon whom be peace, to take either a stipulated amount of alms from the believers’ holdings in the form of the obligatory zakah, or a voluntary, unstipulated amount (zakah of tatawwul). In this ‘ayah, “purify” means to purify them from stinginess, greed, and meanness, and a lack of remorse toward the poor and the wretched. To sanctify them is to raise them in esteem through good deeds and blessings so that they will be worthy of happiness both now and in the afterlife.