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" or "the charity of Ramadan, upon every male and female, free and slave: one sa' of dates or barley," and the people considered it equal to half a sa' of wheat. Ibn Umar (may Allah be pleased with them both) used to give dates; then the people of Madinah ran short of dates, so he gave barley. And he used to give on behalf of every young and old, even on behalf of the sons of Nafi'.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الزكاة / 7678