Muhammad bin Abd al-Rahman al-Ansari states that when Umar bin Abd al-Aziz assumed the caliphate, he sent word to Madinah that the covenant of the Prophet (peace and blessings be upon him) concerning zakah should be searched for. So they found with the family of Amr bin Hazm the letter which the Prophet (peace and blessings be upon him) had written to Amr bin Hazm concerning zakah, and with the family of Umar bin al-Khattab they found the letter which Sayyiduna Umar had written to his agents, and it was exactly in accordance with the letter of the Prophet (peace and blessings be upon him). So Umar bin Abd al-Aziz ordered that zakah be collected according to it. It was also written in it that when there are more than ninety camels, up to one hundred and twenty, two three-year-old she-camels (hiqqah) are due; and when there are more than one hundred and twenty, up to one hundred and twenty-nine, three two-year-old she-camels (bint labun) are due; and when the camels are more than that, nothing is due on an increase of fewer than ten until (the increase) reaches ten. As for the letter of the Prophet (peace and blessings be upon him) written to Amr bin Hazm, its chain meets the condition of this book, and that is why I have mentioned this entire account.