Regarding the following verse from the Holy Quran:
You are the best of the communities raised up for the people; you enjoin good and forbid evil and believe in Allah; and if the followers of the Book were to believe, it would be better for them; from them (few) are Momineen, but most of them are transgressors. [3:110]
When the above verse was recited in the presence of Abu Abdullah (as), he (as) said:
(Are you saying that) the best of the communities are the murderers of Amir-al-momineen (as), and Hasan (as), Husayn (as) the two sons (as) of Ali (as)?
So the reciter said: May I be sacrificed for you (as)! Then how was this verse revealed?
He (as) said: It was revealed – “You are the best of the Imams raised up for the people“. They (as) are the Progeny (as) of Muhammad (s). [Tafsir Al Qummi 110:1 and Tafsir Al Ayyashi 128/195:1]
In another hadith on the same verse, it has been narrated from the 6th Imam (as):
This verse was revealed unto Muhammad (s) regarding himself (s) and regarding the successors (as) in particular, so Allah (swt) said “You are the best of the Imams raised up for the people; you enjoining the good and forbid the evil and believe in Allah [3:110] – It is like this, by Allah, that, Jibraeel descended with it, and it does not mean by it anyone except for Muhammad (s) and his (s) successors (as).
[Reference: Tafsir Al Ayyashi 129/195:1]