Musnad Ahmad 27:143

Sufyan narrated to us, from ‘Amr, from Isma’il al-Shaybani: I sold what was on the tops of my date palms for one hundred wasqs; if it increased, it was theirs, and if it decreased, it was theirs. So I asked Ibn ‘Umar, and he said: "The Messenger of Allah, may Allah bless him and grant him peace, forbade that, but he granted a concession for al-‘araya."