Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) said that the Messenger of Allah (peace and blessings be upon him) "prescribed sadaqat al-fitr as one sa' of dates or barley, upon every free person and slave, old and young."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الزكاة / 7670