Al-Harith says that Sayyiduna Ali bin Abi Talib (may Allah be pleased with him) used to command the payment of sadaqat al-fitr and say: It is a sa' of dates, or barley, or wheat, or hulless barley (sult), or raisins.
It has also been narrated as marfu', but the mawquf version is more authentic.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الزكاة / 7704