Sahih al-Bukhari 1508
Book 24: Obligatory Charity Tax (Zakat) · Narrated by Abu Sa`id Al-Khudri
Arabic
حَدَّثَنَا عَبْدُ اللَّهِ بْنُ مُنِيرٍ، سَمِعَ يَزِيدَ الْعَدَنِيَّ، حَدَّثَنَا سُفْيَانُ، عَنْ زَيْدِ بْنِ أَسْلَمَ، قَالَ حَدَّثَنِي عِيَاضُ بْنُ عَبْدِ اللَّهِ بْنِ أَبِي سَرْحٍ، عَنْ أَبِي سَعِيدٍ الْخُدْرِيِّ ـ رضى الله عنه ـ قَالَ كُنَّا نُعْطِيهَا فِي زَمَانِ النَّبِيِّ صلى الله عليه وسلم صَاعًا مِنْ طَعَامٍ، أَوْ صَاعًا مِنْ تَمْرٍ، أَوْ صَاعًا مِنْ شَعِيرٍ، أَوْ صَاعًا مِنْ زَبِيبٍ، فَلَمَّا جَاءَ مُعَاوِيَةُ وَجَاءَتِ السَّمْرَاءُ قَالَ أُرَى مُدًّا مِنْ هَذَا يَعْدِلُ مُدَّيْنِ.
English translation
Narrated Abu Sa`id Al-Khudri:In the lifetime of the Prophet (ﷺ) we used to give one Sa' of food or one Sa' of dates or one Sa' of barley or one Sa' of Raisins (dried grapes) as Sadaqat-ul-Fitr. And when Muawiya became the Caliph and the wheat was (available in abundance) he said, "I think (observe) that one Mudd (of wheat) equals two Mudds (of any of the above mentioned things)
Reference: Sahih al-Bukhari 1508, Book of Obligatory Charity Tax (Zakat). English translation by Dr. Muhammad Muhsin Khan.