The Messenger of Allah ﷺ made the zakat of Ramadan obligatory upon every free person and slave, male and female, as one saa of dates or one saa of barley. The people later considered half a saa of wheat to be its equivalent.
أخبرنا عمران بن موسى عن عبد الوارث قال حدثنا أيوب عن نافع
فرض رسول الله ﷺ زكاة رمضان على الحر والعبد والذكر والأنثى صاعا من تمر أو صاعا من شعير فعدل الناس به نصف صاع من بر
Bukhari related it in the Book of Zakat, Chapter on Zakat al-Fitr for the free person and the slave, hadith no. 1511, and Muslim in the Book of Zakat, Chapter on Zakat al-Fitr owed by Muslims in dates and barley, hadith no. 14/984, from the hadith of Ayub Sakhtiyani, through this same chain. It is also found in Al-Kubra, hadith no. 2279.