Sahih al-Bukhari 6712
Sahih al-Bukhari · Book 84: Expiation for Unfulfilled Oaths · The Sa' of Al-Madina, and the Mudd of the Prophet (saws)
Narrated Al-Ju'aid bin `Abdur-Rahman:
حَدَّثَنَا عُثْمَانُ بْنُ أَبِي شَيْبَةَ ، حَدَّثَنَا الْقَاسِمُ بْنُ مَالِكٍ الْمُزَنِيُّ ، حَدَّثَنَا الْجُعَيْدُ بْنُ عَبْدِ الرَّحْمَنِ ، عَنِ السَّائِبِ بْنِ يَزِيدَ ، قَالَ كَانَ الصَّاعُ عَلَى عَهْدِ النَّبِيِّ صلى الله عليه وسلم مُدًّا وَثُلُثًا بِمُدِّكُمُ الْيَوْمَ فَزِيدَ فِيهِ فِي زَمَنِ عُمَرَ بْنِ عَبْدِ الْعَزِيزِ .
As-Sa'ib bin Yazid said, "The Sa' at the time of the Prophet (ﷺ) was equal to one Mudd plus one-third of a Mudd of your time, and then it was increased in the time of Caliph `Umar bin `Abdul `Aziz."