It is narrated from Sayyiduna Tha'labah bin Su'ayr (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) stood up to deliver a sermon and commanded Sadaqat al-Fitr, upon the young and the old, the free and the slave: one sa' of dates or one sa' of barley on behalf of each person, or on behalf of each head, and one sa' of wheat on behalf of two people.
Hadith Referenceالمعجم الكبير للطبراني / باب الثاء / 1376