Hadith 5:169
Hafs narrated to us, from Layth, from Nafi’, from Ibn ‘Umar, that ‘Umar, when he would send the tax collector (al-musaddiq), he would send with him a document in which it was written: "There is nothing (due) in less than forty sheep."
حدثنا حفص عن ليث عن نافع عن بن عمر أن عمر كان إذا بعث المصدق بعث معه بكتاب فيه ليس في أقل من أربعين شاة شيء