Nafi' narrates from Ibn Umar (may Allah be pleased with them both) that the Messenger of Allah (peace and blessings be upon him) "prescribed sadaqat al-fitr as one sa' of dates and barley on behalf of every young and old, free and slave."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الزكاة / 7675