Musnad Ahmad 31:707

'Abd al-Razzaq narrated to us, Sufyan informed us, from Zayd ibn Aslam, 'Iyad ibn 'Abd Allah ibn Sa'd ibn Abi Sarh narrated to us, from Abu Sa'id al-Khudri, who said: "We used to pay the Sadaqat al-Fitr during the time of the Messenger of Allah (peace and blessings of Allah be upon him) as a sa' of barley, a sa' of dates, a sa' of raisins, and a sa' of dried yogurt (aqit). When Mu'awiyah came, and wheat (al-samra') came, he saw that one mudd [of wheat] was equivalent to two mudds [of the other items]."