بسم الله الرحمن الرحيم
Shaykh Salih Alish-Shaykh says: The reviling of every companion is disbelief because Allah has spoken good of them, He says:
..محمد رسول الله و الذين معه أشداء على الكفار رحماء بينهم تراهم ركعاً سجداً يبتغون فضلاً من الله و رضواناً سيماهم في وجوههم من أثر السجود
“Muhammad is the Messenger of Allah, and those with him are stern against the disbelievers yet merciful among themselves. You see them bowing and prostrating sincerely seeking Allah’s bounty and pleasure. Their sign is on their faces from the traces of prostration…” [Al-Fath: 29]
The Exalted also says:
لقد رضي الله عن المؤمنين إذْ يبايعونك تحت الشجرة
Indeed, Allah was pleased with the believers when they gave you the pledge under the tree…” [Al-Fath: 18]
In addition the Prophet -sallahu alayhi wa salaam- said, “Do not insult anyone from my companions. I swear by Him in whose hand is my soul if anyone of you were to spend the like of mount Uhud in gold you would neither reach a dry bushel of anyone from among them (as it relates to virtue) nor half that.” So whoever insults the companions rejects Allah’s praise of them, and denies what is explicit in the Quran which is disbelief from which Allah’s refuge is sought.
Also the revilement of the tabi’een is evil, a major sin, and prohibited. It is possible for it to be deemed disbelief due to them being the best generation (of Muslims) after the companions’ generation, and this is established by way of the testimony of the most noble and truthful of creation, the Prophet -sallahu alayhi wa salaam- where he said, “The best of mankind (are in) my generation, then those that succeed them, and then those that succeed them…”
Translated by Najeeb Al Anjelesi
Source: المنظار في بيان كثير من الأخطاء الشائعة