Sahih Muslim
The Book of Zakat (Kitab Al-Zakat)
Book Number: 005 / Hadith Number: 2139
Abu Sa'id al-Khudri reported Allah's Messenger (may peace be upon him) as saying: No Sadaqa is payable on the grains and dates till it (comes to the Weight) of five wasqs, or less than five heads of camels, or less than five uqiyas (of silver).