al-Hasan al-Basri الحسن البصري · The Book of Zakah

the Messenger of Allah enjoined Zakatul-Fitr at the end of Ramadan upon the people; a Sa' of dates or a Sa' of barley, upon everyone, free or slave, male or female, of the Muslims.

I heard Ibn 'Abbas deliver a Khutbah from your Minbar - meaning the Minbar in Al-Basrah - saying: 'Sadaqatul Fitr is a Sa' of food." (Sahih) Abu 'Abdur-Rahman (An-Nasa'i) said: This is the most reliable of the three.

"At the time of the Messenger of Allah, the people used to give as Sadaqatul Fitr a Sa' of barely or dates or rye or raising."