Bukhari

Hadith Commentary:
For this reason, the Kufan mudd and sa’ are not reliable.

Hadith Commentary:
(1)
There are four mudd in one sa’ (sā‘).
In the time of the Messenger of Allah (sallallahu alayhi wa sallam), the measure of a mudd was 1 and 1/3 ratl, thus the measure of the Prophetic sa’ (sā‘ nabawi) was 5 and 1/3 ratl.
However, during the era of Banu Umayyah, Hisham introduced another mudd which was two-thirds larger than the mudd of the Messenger of Allah (sallallahu alayhi wa sallam). Nevertheless, Ibn Umar (radi Allahu anhu) paid no attention to this mudd and continued to use the original mudd.
Hafiz Ibn Hajar (rahimahullah) writes:
The mudd introduced by Hisham was two-thirds of a ratl greater than the mudd of the Messenger of Allah (sallallahu alayhi wa sallam), and its measure was two ratl. Accordingly, the sa’ was equivalent to eight ratl, whereas the mudd of the Messenger of Allah (sallallahu alayhi wa sallam) was 1 and 1/3 ratl and the sa’ was 5 and 1/3 ratl.
(Fath al-Bari: 11/729) (2)
Generally, the sa’ of the Messenger of Allah (sallallahu alayhi wa sallam) is called the Hijazi sa’ (sa‘ Hijazi), and the sa’ of Banu Umayyah is called the Baghdadi sa’ (sa‘ Baghdadi) or the Iraqi sa’ (sa‘ ‘Iraqi), and the Iraqi sa’ is one-third larger than the Hijazi sa’.
The Hanafis considered the mudd and sa’ introduced by Banu Umayyah as the standard, whereas the hadith scholars (muhaddithin) considered the Hijazi sa’ as authoritative.
In this regard, the following incident is of landmark significance. It is narrated from Husayn ibn Walid Qurashi, who said:
After completing Hajj, Imam Abu Yusuf (rahimahullah) came to us and said: I wish to open for you a door to important knowledge regarding which I have conducted thorough research.
The incident is as follows: I went to Madinah Tayyibah and inquired from the people about the sa’. They replied:
Our sa’ is the same as the sa’ of the Messenger of Allah (sallallahu alayhi wa sallam).
I asked for proof of this claim, and they said:
Tomorrow we will present its proof.
The next day, about fifty elders from among the descendants of the Ansar and Muhajirin came to me, each with a sa’ under his cloak.
Each one narrated the chain of transmission of this sa’ back to the Messenger of Allah (sallallahu alayhi wa sallam).
When I examined them, they were all identical.
When I weighed them, each sa’ weighed 5 and 1/3 ratl.
After this, I considered the statement of the people of Madinah regarding the sa’ to be correct and strong, and I abandoned the opinion of my teacher Abu Hanifah (rahimahullah).
(Al-Sunan al-Kubra lil-Bayhaqi: 4/171)