Sayyiduna Abu Sa'id Khudri (may Allah be pleased with him) narrates: When the Prophet (peace and blessings of Allah be upon him) was among us, we used to give one sa' of grain, or one sa' of dates, or one sa' of barley, or one sa' of cheese as Sadaqat al-Fitr. This continued in the same way until Sayyiduna Mu'awiyah (may Allah be pleased with him) came from Syria to Madinah during his rule. He discussed this matter with the people and said: I think that two mudd of wheat from Syria are equal to one sa', so the people adopted this.
Hadith Referenceصحیح ابن حبان / كتاب الزكاة / 3305
Hadith Gradingفضيلة الشيخ الإمام محمد ناصر الدين الألبانيصحيح - «صحيح أبي داود» (1433): م.فضيلة الشيخ العلّامة شُعيب الأرناؤوطإسناده صحيح على شرط مسلم