Ishaq bin Ibrahim bin Muhammad إسحاق بن إبراهيم بن محمد · The Book of Zakah

"The Messenger of Allah sent me to Yemen and he commanded me to take one-tenth of whatever is irrigated by the sky, and half of one-tenth of whatever is irrigated by means of buckets."

"The Messenger of Allah enjoined Zakah of Ramadan upon the free and the slave, male and female, a Sa of dates or a Sa of barley, so the people considered that equivalent to half a Sa of wheat."

"I heard that you have been doing some work for the Muslims, and you are given payment for that, but you do not accept it. "I said: "Yes (that is so); I have horses and slaves and am well-off, and I wanted my work to be an act of charity toward the Muslims." 'Umar, may Allah be pleased with him, said: "I wanted the same thing as you. The Prophet used to give me money, and I would say: 'Give…

"I heard that you do some jobs for the people but when payment is given to you, you refuse it." I said: "(that is so)." 'Umar, may Allah be pleased with him, said: "Why do you do that? I said: "I have horses and slaves and am well off, and I wanted my work to be an act of charity toward the Muslims." 'Umar said to him: "Do not do that. I used to want the same thing as you.…