Sahih Bukhari Volume 2, Book 25, Hadith Number 586.

Narated By Abu Said Al-Khudri : In the life-time of Allah’s Apostle , we used to give one Sa’ of food (edible things) as Sadaqat-ul-Fit,r (to the poor). Our food used to be either of barley, raisins (dried grapes), cottage cheese or dates.