He traced it back to the Prophet ﷺ, who said, "There is no zakat on anything less than five wasqs, and a wasq is sixty makhtums."
حدثنا يعلى حدثنا إدريس الأودي عن عمرو بن مرة عن أبي البختري
يرفعه إلى النبي ﷺ قال ليس فيما دون خمسة أوساق زكاة والوسق ستون مختوما
Its isnad is sahih. There is some discussion regarding Abu Bakhtari's hearing from Abu Saeed, but he explicitly stated hearing from him on several occasions, and there were only ten years between their deaths. Idris is Ibn Yazid, and Abu Bakhtari is Saeed bin Firuz, and all of them are trustworthy. The hadith has already appeared at 11343.His statement "sixty, sealed" is from the words of the narrator, by which he means that a wasq is sixty sa, sealed, that is, filled.