The Prophet ﷺ ordered (Muslims) to give one Sa' of dates or one Sa' of barley as Zakat-ul-Fitr. The people rewarded two Mudds of wheat as equal to that.  

أَمَرَ النَّبِيُّ ﷺ بِزَكَاةِ الْفِطْرِ صَاعًا مِنْ تَمْرٍ أَوْ صَاعًا مِنْ شَعِيرٍ قَالَ عَبْدُ اللَّهِ ؓ فَجَعَلَ النَّاسُ عِدْلَهُ مُدَّيْنِ مِنْ حِنْطَةٍ