Abu Sa'id al-Khudri (may Allah be pleased with him) said that the Messenger of Allah (peace and blessings be upon him) said: "There is no zakah on less than five uqiyah, nor is there zakah on less than five camels." Sufyan said: An uqiyah is forty dirhams.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الزكاة / 7244