Sayyiduna Abu Sa'id al-Khudri (may Allah be pleased with him) narrates from the Prophet (peace and blessings be upon him) as marfu' that he (peace and blessings be upon him) said: "There is no zakah on less than five wasq, and a wasq is sixty sa'."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الزكاة / 7427