Fiqh-us-Sunnah Volume 3, Zakaat and Fasting, Fiqh 3.087A.
Section : The Purpose of Zakat ul-Fitr.
Zakat ul-fitr was made obligatory in the month of Sha’ban in the second year of the hijrah. Its purpose is to purify one who fasts from any indecent act or speech and to help the poor and needy. This view is based upon the hadith reported by Abu Dawud, Ibn Majah, and ad-Daraqutni from Ibn ‘Abbas. The Messenger of Allah, upon whom be peace, enjoined zakat ul-fitr on the one who fasts to shield one’s self from any indecent act or speech and for the purpose of providing food for the needy. It is accepted as zakah for the person who pays it before the ‘id salah, and it is sadaqah for the one who pays it after the salah.