Musannaf Ibn Abi Shayba 13:737

Abu Bakr narrated to us, he said: Ibn Abi Za'idah narrated to us, from Ubayd Allah ibn Umar, from Nafi', from Ibn Umar, that the Prophet (peace and blessings of Allah be upon him) forbade the selling of dates for dates by measure, and the selling of grapes for raisins by measure, and the selling of crops for wheat by measure.