Sunan an-Nasa'i, Volume 3, Book 23, Hadith 2504 (DarusSalam) ⓘ
It was narrated that Ibn 'Umar said: "The Messenger of Allah enjoined the Zakah of Ramadan on everyone, young and old, free and slave, male and female, a Sa of dates or a Sa of barley."
أَخْبَرَنَا قُتَيْبَةُ، قَالَ حَدَّثَنَا مَالِكٌ، عَنْ نَافِعٍ، عَنِ ابْنِ عُمَرَ، قَالَ فَرَضَ رَسُولُ اللَّهِ صلى الله عليه وسلم زَكَاةَ رَمَضَانَ عَلَى كُلِّ صَغِيرٍ وَكَبِيرٍ حُرٍّ وَعَبْدٍ وَذَكَرٍ وَأُنْثَى صَاعًا مِنْ تَمْرٍ أَوْ صَاعًا مِنْ شَعِيرٍ .
also referenced under: Hadith 2502 (Reference) & Book 23, Hadith 0 (In-Book)