Messenger of Allah ﷺ has made Sadaqat-ul-Fitr obligatory, (and it was), either one Sa' of barley or one Sa' of dates (and its payment was obligatory) on young and old people, and on free men as well as on slaves.  

فَرَضَ رَسُولُ اللَّهِ ﷺ صَدَقَةَ الْفِطْرِ صَاعًا مِنْ شَعِيرٍ أَوْ صَاعًا مِنْ تَمْرٍ عَلَى الصَّغِيرِ وَالْكَبِيرِ وَالْحُرِّ وَالْمَمْلُوكِ