And Imâm Ahmad Ibn Hanbal said in his book As-Sunnah:
“It is not permissible for anyone to mention any of their faults, nor may anyone disparage any of them. Whoever does that, the governmental authority is obligated to reprimand and punish him. He is not to pardon him, but rather he must punish him and then request him to repent. If he repents, he should accept it from him, but if he doesn't repent, he should reinitiate the punishment upon him and lock him in prison forever until he repents and recants (from his false beliefs).
Imâm Abu 'Uthmân As-Sâbûnî said in his book 'Aqîdat-us-Salaf wa Ashâb-il-Hadîth:
“And they held it an obligation to refrain from (speaking about) the differences that occurred between the Companions of Allâh's Messenger (peace and blessing be upon him) and to purify the tongues from mentioning anything that consists of a blemish on them or a degradation of them. They held it an obligation to ask Allâh for mercy for all of them and to show allegiance to all of them.”
Shaikh-ul-Islâm Ibn Taimiyyah said in his book Al-'Aqîdat-ul-Wâsitiyyah:
“Among the Principles of Ahl-us-Sunnah wal-Jamâ'ah is maintaining pure hearts and tongues towards the Companions of Allâh's Messenger (peace and blessing be upon him), as Allâh described them in His saying:
‘And those who come after them say: ‘Our Lord! Forgive us and our brothers who preceded us in Faith. And put not in our hearts any hatred against those who have believed. Our Lord, You are indeed full of kindness, most Merciful.’ [Sûrah Al-Hashr: 8-10].
And (from their principles is) obedience to the Prophet (peace and blessing be upon him) with regard to his saying:
‘Do not revile my Companions! For by the One whose Hand my soul is in, if one of you were to give away the size of mount Uhud in gold for charity, it would not equal a mudd of one of them nor even half of it.’
They accept what is stated in the Qur'ân, the Sunnah and the Consensus concerning their (the Companion's) virtues and high status. They give preference to those who spent their wealth and fought (in the Way of Allâh) before the Victory - which refers to the Treaty of al-Hudaybiyah - over those who gave their wealth and fought after it. They give precedence to the Muhâjirîn over the Ansâr, and they believe that Allâh said to the people who fought in (the Battle of) Badr - who numbered over three hundred people:
‘Do whatever you wish, for I have already forgiven you.’
They believe that no one who pledged their allegiance to the Prophet (peace and blessing be upon him) under the tree will enter the Hellfire, as the Prophet (peace and blessing be upon him) informed us. In fact, Allâh was pleased with them and they were pleased with Him, and they were more than one thousand four hundred people.
They designate to Paradise whoever the Messenger of Allâh (peace and blessing be upon him) testified will be in Paradise, such as the Ten (Companions), Thâbit Ibn Qays Ibn Shammas and others.