Volume 2 · Book 25 · Hadith 580
Narrated Ibn 'Umar: Allah's Apostle made it incumbent on all the slave or free Muslims, male or female, to pay one Sa' of dates or barley as Zakat-ul-Fitr.
— Sahih Bukhari, Volume 2, Book 25: Obligatory Charity Tax After Ramadaan (Zakat ul Fitr), Hadith #580