Ahmad Ibn Hanbal said:
“It is from the Sunnah to mention the good qualities of the Companions of the Messenger of Allaah (saw), all of them, without exception…
So whoever insults the Companions of the Messenger of Allaah (saw), even one Companion from among them, then he is an innovator, a filthy, bankrupt Raafidhee. Allaah will not accept even one of his deeds…
Rather, loving them is Sunnah,
Supplicating for them is a good deed that brings one close (to Allaah),
Following their example is a means (to success),
And embracing their ways of guidance is a virtue…
And the Companions of the Messenger of Allaah (saw) – after the four caliphs – are the best of the people, and it is not permissible for anyone to … speak ill of any of them, blaming them for deficiencies and shortcomings.
It is indeed obligatory upon the ruler to reprimand and punish whoever does that, and he should not be pardoned.”
[Kitaab As-Sunnah, p. 77-78 & Manaaqibul Imaam Ahmad, of Ibnul Jawzee, p. 170]