Sahih Bukhari
Expiation for Unfulfilled Oaths
Volume: 008 / Book Number: 079 / Hadith Number: 703
Narrated Al-Ju'aid bin Abdur-Rahman:
As-Sa'ib bin Yazid said, "The Sa' at the time of the Prophet 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."