Musnad Ahmad 27:43

Isma'il narrated to us, Ayyub informed us, from Nafi', from Ibn Umar: "That the Messenger of Allah (ﷺ) forbade al-muzabanah. And al-muzabanah is that what is in the tops of the palm trees be sold for dates by a specified measure; if it increases, it is for me, and if it decreases, it is upon me." Ibn Umar said: Zayd ibn Thabit narrated to me that the Messenger of Allah (ﷺ) "granted a concession in the sale of al-'araya by its estimation."