Sunan Ibn Majah, Chapter: The Chapters Regarding Zakat

when the Prophet (saw) conquered Khaibar, he stipulated that the land, and all the yellow and white, meaning gold and silver belonged to him. The people of Khaibar said to him: "We know the land better, so give it to us so that we may work the land, and you will have half of its produce and we will have half." He maintained that, he gave it to them on that basis. When the time for the date harvest came, he sent Ibn Rawahah to them. He assesses the date palms, and he said: "For this tree, such and such (amount)." They said: "You are demanding too much of us, O Ibn Rawahah!" He said: "This is my assessment and I will give you half of what I say." They said: "This is fair, and fairness is what haven and earth are based on." They said: "We Agree to take (accept) what you say." Sahih