[AmfitNom]

As Salamu Alaikum

(I explained this before in another thread, here is a copy of it)
Imam al-Ashari (ra) was throughout his life a Mutazilite until at the age of 40 when he openly denounced the Mutaziliite beliefs and challenged them as they had the most influence in the Muslim world at that time. The differences between Imam al-Ashari (ra) and Imam al-Maturidi (ra) is really geographical and in methodology and not in the fundamentals. Al-Ashari (ra) was closer in contact with the elite of the Mutazilites and would challenge them.

Regarding methodology, I will quote from Imam Abu Hanifa's Al-Fiqh Al-Akbar Explained:

"Ashari did not give much preference to reason in the presence of sacred texts, even if they were transmitted by lone narrators rather than through uninterrupted transmission, while Maturidi would attempt to reconcile between reason and the transmitted texts, as long as it was possible to do so without too much difficulty or without sacrificing fairness." There are three accepted schools of creed from the Ahl-ul-Sunnah: Ash'ari, Maturidi and Athari according to the opinion of Al-Saffarini (ra).

The dividing opinions comes between modern day Salafis (only Athari creed are Ahl-ul-Sunnah) vs. non-Salafis (only Ash'ari/Maturidi are Ahl-ul-Sunnah)

The opinion of Al-Saffarini (ra) is acceptable as the Ash'ari's and Maturidi's were established schools AGAINST the Mutazilites, something Salafis will not recognize. The Athari creed can be acceptable based on one Tab'ien (may Allah be pleased with him), who believed textualism of Qur'an. The major difference is that from my understanding the Athari school is not an established school, that even Ibn Taymiyah (ra) and Ibn Kathir (ra) had differences of opinion, and the possible innovation of the belief of Allah's "Left Hand" was established by the Khalaf (unless someone can provide Proof please that Allah and his Messenger salalahu alahi wasalam ever said the word "Left Hand" in Qur'an and Hadith in regards to Allah).

Allah knows best.