It is narrated from Sayyiduna Ibn Abbas (may Allah be pleased with them both) that when the Prophet (peace and blessings be upon him) conquered Khaybar, he stipulated to them that the land and everything yellow and white, meaning gold and silver, would be his. The people of Khaybar said to him: "We know the land better, so give it to us; we will work it, and half of the fruit will be ours and half yours." He gave them the land of Khaybar on that condition. When it was time for the date palms to be harvested, he sent Ibn Rawahah (may Allah be pleased with him) to them, and he estimated the date palms, which the people of Madinah call al-khars. Ibn Rawahah (may Allah be pleased with him) said: "In this there is such and such." They said: "O Ibn Rawahah, you have overestimated." Ibn Rawahah (may Allah be pleased with him) said: "Then I will take the date palms and give you half of what I said." They said: "This is the truth by which the heavens and the earth stand; we are content to take it at what you have said."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب المساقاة / 11628