Musnad Ahmad 31:485

'Abd al-Malik narrated to us, Hisham and Yazid ibn Harun narrated to us, Hisham informed us, from Yahya, from Abu Salamah, from Abu Sa'id al-Khudri, who said: We used to be provided with *tamr al-jam'*—and Yazid said: "dates from the dates of *al-jam'"—during the time of the Messenger of Allah (peace and blessings of Allah be upon him), and we would sell two *sa'* for one *sa'*. This reached the Prophet (peace and blessings of Allah be upon him), so he said: "Do not [sell] two *sa'* of dates for one *sa'*, nor two *sa'* of wheat for one *sa'*, nor two dirhams for one dirham."