Bukhari

Hadith Commentary:
Perhaps Uthman (radi Allahu anhu) considered tamattu‘ (combining Hajj and ‘Umrah in one journey) to be objectionable due to following Umar (radi Allahu anhu), and he also thought that the command of the Prophet (sallallahu alayhi wa sallam) to annul the Hajj and perform ‘Umrah was specific to the Companions (radi Allahu anhum).
Some have said that he considered it mildly disliked (makruh tanzihi), and since this opinion of Uthman (radi Allahu anhu) was contrary to the hadith,
therefore Ali (radi Allahu anhu) did not act upon it and said: “I cannot leave the hadith of the Prophet (sallallahu alayhi wa sallam) for anyone’s statement.”
O Muslim brothers! Just look carefully at this statement of Ali (radi Allahu anhu): Uthman (radi Allahu anhu) was the caliph of the time—and what a caliph! A rightly guided caliph and the Commander of the Faithful (Amir al-Mu’minin).
But his statement, being against the hadith, was set aside, and his contrary was acted upon right in front of him.
Then what has happened to you that you continue to hold on to the statements of Abu Hanifah or Shafi‘i, and act upon their statements in opposition to authentic hadith? This is clear misguidance.
For the sake of Allah, refrain from this and accept what we say. We have conveyed to you what was the truth; now the choice is yours.
On the Day of Judgment, when you stand before the Prophet (sallallahu alayhi wa sallam), present your excuse. And peace. (Maulana Waheeduz-Zaman, rahimahullah)

Hadith Commentary:
(1)
This meeting between Hazrat Uthman and Hazrat Ali (radi Allahu anhuma) took place at the location of Usfan.
(Sahih al-Bukhari, Book of Hajj, Hadith: 1569)
(2)
Hazrat Uthman (radi Allahu anhu) used to prohibit both tamattu‘ and qiran so that people would not completely neglect ifrad Hajj.
It is also possible that he only prohibited qiran Hajj, and it is called tamattu‘ because the one performing qiran is spared the hardship of making a separate journey for ‘umrah; in this way, he attains the benefit of performing both Hajj and ‘umrah in a single journey.
Since Hazrat Uthman’s (radi Allahu anhu) prohibition was based on his own ijtihad (independent reasoning), Hazrat Ali (radi Allahu anhu) did not act upon it; rather, he said that the command of the Messenger of Allah (sallallahu alayhi wa sallam) cannot be abandoned on account of anyone’s statement.
(3)
From this hadith, it is also understood that Hazrat Uthman (radi Allahu anhu) was very forbearing and gentle-natured.
This is why, despite being the caliph, he did not reproach anyone for this opposition.
(4)
From a narration in Sunan al-Nasa’i, it is understood that Hazrat Uthman (radi Allahu anhu) had retracted from this position.
(Sunan al-Nasa’i, Manasik al-Hajj, Hadith: 2724)
However, this retraction is not in explicit words, but rather, the narration indicates a retraction.
(Fath al-Bari: 3/536)
(5)
From this hadith, the importance of following the Sunnah is evident, as the noble Companions (radi Allahu anhum) did not give precedence to the ijtihad of any Companion over the hadith of the Messenger of Allah (sallallahu alayhi wa sallam).
For those who abandon an explicit hadith simply because our imam, mufti, or elder has not given a fatwa upon it, this is a point of reflection.