(70) باب فَرْضِ صَدَقَةِ الْفِطْرِ
Narrated Ibn `Umar:
Allah's Messenger (ﷺ) enjoined the payment of one Sa' of dates or one Sa' of barley as Zakat-ul-Fitr on every Muslim slave or free, male or female, young or old, and he ordered that it be paid before the people went out to offer the `Id prayer. (One Sa' = 3 Kilograms approx.)
Reference: Sahih al-Bukhari 1503
In-book reference: Book 24, Hadith 104
USC-MSA web (English) reference(deprecated numbering scheme): Vol. 2, Book 25, Hadith 579