Abu Sa'id al-Khudri reported Allah's Messenger (ﷺ) as saying:
No Sadaqa (zakat) is due on less than five wasqs of (dates or grains), on less than five camel-heads, and on less than five uqiyas (of silver). (ID)
Reference (ID): Sahih Muslim 979 d (ID)
In-book reference (ID): Book 12, Hadith 4 (ID)
USC-MSA web (English) reference(deprecated numbering scheme): Book 5, Hadith 2137 (ID)