"The Messenger of Allah (PBUH) ordained Zakat al-Fitr (Fitrana) to purify the fasting person from indecent words or actions and to provide food for the needy. It is accepted as Zakat for the person who gives it before the Eid prayer, but it is a mere Sadaqah for the one who gives it after the prayer."
(Abu Dawud, Ibn Majah)