Musannaf Ibn Abi Shaybah

Hazrat Ibn Umar (may Allah be pleased with them both) narrates that when the Holy Prophet (peace and blessings be upon him) wrote about Zakat, he placed it with his sword, or (the narrator is in doubt) did not take out that written document with his will until his death. Then after him, Hazrat Abu Bakr Siddiq acted upon it until his death, and then after him, Hazrat Umar acted upon it until his death. It was written in it: When camels exceed one hundred and twenty, then for every fifty, one Hiqqah and for every forty, one Bint Laboon is due as Zakat.