Sunan Ibn Majah
1825
Sahih+3

Ibn Umar narrated that:the Messenger of Allah enjoined Zakatul-Fitr, one Sa of dates or one Sa of barley.Abdullah said: The people made two Mudd (equal to half of a Sa) of wheat as its equivalent

SahihAl-Albani
SahihMuhammad Fouad Abd al-Baqi