Obligatory Charity Tax After Ramadaan (Zakat ul Fitr)

Bukhari :: Book 2 :: Volume 25 :: Hadith 588

Narrated Ibn 'Umar:

Allah's Apostle has made Sadaqatul-Fitr obligatory, (and it was), either one Sa' of barley or one Sa' of dates (and its payment was obligatory) on young and old people, and on free men as well as on slaves.