Sahih Muslim
The Book of Zakat (Kitab Al-Zakat)
Book Number: 005 / Hadith Number: 2137
Abu Sa'id al-Khudri reported Allah's Messenger (may peace be upon him) as saying: Sadaqa (zakat) is payable on less than five wasqs of (dates or grains), on less than five camel-heads, and on less than five uqiyas (of silver).