Sunan Ibn Majah, Book 8, Hadith 43 (In-Book) ⓘ
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.
حَدَّثَنَا مُحَمَّدُ بْنُ رُمْحٍ الْمِصْرِيُّ، حَدَّثَنَا اللَّيْثُ بْنُ سَعْدٍ، عَنْ نَافِعٍ، عَنِ ابْنِ عُمَرَ، أَنَّ رَسُولَ اللَّهِ ـ صلى الله عليه وسلم ـ أَمَرَ بِزَكَاةِ الْفِطْرِ صَاعًا مِنْ تَمْرٍ أَوْ صَاعًا مِنْ شَعِيرٍ . قَالَ عَبْدُ اللَّهِ فَجَعَلَ النَّاسُ عِدْلَهُ مُدَّيْنِ مِنْ حِنْطَةٍ .
also referenced under: Hadith 1825 (Reference) & Volume 3, Book 8, Hadith 1825 (DarusSalam)