Abu Sa'id al-Khudri (may Allah be pleased with him) said that he heard the Messenger of Allah (peace and blessings be upon him) say: "There is no zakah on less than five wasqs of dates, nor is there zakah on less than five uqiyahs of silver, nor is there zakah on less than five camels." Abu Usamah was asked to confirm this, and he said: Yes, that is so.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الزكاة / 7516