It is narrated from Abdullah bin Umar (may Allah be pleased with them both) that he (peace and blessings be upon him) said: "Sadaqat al-fitr is obligatory upon every slave and free person among the Muslims: a sa' of dates or of barley."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الزكاة / 7690