Sunan an-Nasa'i, Hadith 2501 ⓘ
It was narrated that Ibn 'Umar said: "The Messenger of Allah enjoined Sadaqatul Fitr upon male and female, free and slave; a Sa of dates or a Sa of barley." He said: "The people considered that equivalent to half a Sa of wheat."
أَخْبَرَنَا قُتَيْبَةُ، قَالَ حَدَّثَنَا حَمَّادٌ، عَنْ أَيُّوبَ، عَنْ نَافِعٍ، عَنِ ابْنِ عُمَرَ، قَالَ فَرَضَ رَسُولُ اللَّهِ صلى الله عليه وسلم صَدَقَةَ الْفِطْرِ عَلَى الذَّكَرِ وَالأُنْثَى وَالْحُرِّ وَالْمَمْلُوكِ صَاعًا مِنْ تَمْرٍ أَوْ صَاعًا مِنْ شَعِيرٍ . قَالَ فَعَدَلَ النَّاسُ إِلَى نِصْفِ صَاعٍ مِنْ بُرٍّ .
also referenced under: Book 23, Hadith 0 (In-Book) & Volume 3, Book 23, Hadith 2503 (DarusSalam)