Abu Raja' (may Allah have mercy on him) says: I heard Ibn Abbas (may Allah be pleased with them both) delivering a sermon from the pulpit, saying about sadaqat al-fitr that it is a sa' of food.
This is the correct version, and it is mawquf.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الزكاة / 7705