Sayyiduna Ibn Abbas (may Allah be pleased with them both) narrated: "The Messenger of Allah (peace and blessings be upon him) paid an expiation with a sa' of dates, and he ordered the people to do the same; and whoever cannot find a sa' should give half a sa'."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 12218