Abu Bakr bin Muhammad bin Amr bin Hazm narrates from his father, and he from his grandfather (may Allah be pleased with him), that the Prophet (peace and blessings be upon him) wrote a letter to the people of Yemen, and in this hadith he mentioned: "On every five grazing camels there is one sheep, until they reach twenty-four. And in it also: On every forty grazing sheep there is one sheep, until they reach one hundred and twenty. If they exceed that by one, then instead of one sheep there are two sheep."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الزكاة / 7389