We used to take out as the Zakat of Fitr one sa' of grain, or one sa' of barley or one sa' of dates, or one sa' of cheese or one sa' of raisins.
Sahih Muslim Book 12, Hadith 21
← Previous Hadith Ibn Umar reported that the Messenger of Allah (ﷺ) prescribed Zakat-ul-Fitr of Ramadan one sa' of dates or one sa' of barley for every individual among the Muslims (whether) free man or slave, male or female, young or old.

Sahih Muslim Book 12, Hadith 20 Next Hadith → We, on behalf of every young or old, free man or slave (amongst us), used to take out during the lifetime of the Messenger of Allah (ﷺ) as the Zakat of Fitr one sa' of grain, or one sa' of cheese or one sa' of raisins. And we continued taking out these till Mu'awiya b. Abu Sufyan came to us for pilgrimage or 'Umra, and addressed the people on the pulpit and said to them: I see that two mudds of zakat out of the wheat (red) of Syria is equal to one sa' of dates. So the people accepted it. But Abu Sa'id said: I would continue to take out as I used to take out (before, i e. one sa') as long as I live.

Sahih Muslim Book 12, Hadith 22