Abu Sa'id al-Khudri (may Allah be pleased with him) reports that during the time of the Messenger of Allah (peace and blessings be upon him), we used to give one sa' of dates, raisins, cheese, dried yogurt, or barley as zakat al-fitr. This practice continued until the era of Mu'awiyah (may Allah be pleased with him). He said: I think that two mudd of wheat from Syria are equal to one sa' (of the above items). So the people started acting accordingly.
Hadith Referenceالمنتقى ابن الجارود / كتاب الزكاة / 357
Hadith Gradingغلام مصطفےٰ ظهير امن پوري:صحيح
Hadith Takhrijاز غلام مصطفےٰ ظهير امن پوري:«صحيح البخاري : 1508 ، صحيح مسلم : 985»