Volume 2 · Book 24 · Hadith 538
Narrated Abu Said Al-Khudri : Allah's Apostle said, "No Zakat is imposed on less than five Awsuq of dates; no Zakat is imposed on less than five Awaq of silver, and no Zakat is imposed on less than five camels."
— Sahih Bukhari, Volume 2, Book 24: Obligatory Charity Tax (Zakat), Hadith #538