(4) باب زَكَاةِ الْفِطْرِ عَلَى الْمُسْلِمِينَ مِنَ التَّمْرِ وَالشَّعِيرِ
Ibn Umar reported that the Messenger of Allah (ﷺ) prescribed Zakat-ul-Fitr of Ramadan one sa' of dates or one sa' of barley for every individual among the Muslims (whether) free man or slave, male or female, young or old.
Reference: Sahih Muslim 984 e
In-book reference: Book 12, Hadith 20
USC-MSA web (English) reference(deprecated numbering scheme): Book 5, Hadith 2153