Ibn Ásākir narrates the story of how Imām Al-Ashárī converted to Ahlu’s Sunnah from his former madh’hab of Mútazilah. [Tabyīn Kadhib al-Muftarī fīmā Nusiba ila’l Imām Abu'l Ĥasan al-Ashárī / Exposing the maligner’s lies, in those things falsely attributed to Imām Abu'l Ĥasan al-Ashárī.]

Imām al-Ashárī says: One Ramadan, I saw RasūlAllāh şallAllāhu álayhi wa sallam once, during the first ten days. He said: “O Álī, aid the madh'habs that are veritably reported by me, because only that is the Truth.” I woke up and was perplexed about this grave matter. I was immensely worried about this because I had numerous proofs opposing this ‘reported’ belief.

With the next ten days, I saw him again şallAllāhu álayhi wa sallam. “What did you do about that which I ordered you to do?” I said: “Yā RasūlAllāh, I tried to do it but I have many strong proofs [and arguments] against those beliefs which are reported from you. Therefore I follow that which has stronger proofs concerning [the Attributes] of Allāh táālā” He said: “Aid the madh'habs that are reported from me, because that is the truth”

I woke up and I was terribly saddened. I then forsook Kalām [theology] and began following the ĥadīth and reciting the Qur’ān.

In Basrah we have a custom that reciters (qurrā’a) assemble together on the twenty seventh night of Ramađān and finish the entire Qur’ān in that night [aH: we still have this custom in India; it has a noble precedent after all.] But I was feeling very sleepy and I couldn't stay back any longer. So I returned home and went to sleep, feeling extremely sorry at the great loss of missing that night’s khatm.

I saw RasūlAllāh şallAllāhu álayhi wa sallam again, and he asked: “What did you do about that which I told you?” I replied: “I have forsaken Kalām and taken a firm hold of the Book of Allāh and your sunnah.” He said: “I did not ask you to forsake Kalām. I told you to aid the madh'hab that is reported from me, because that is the truth.”

I said: “Yā RasūlAllāh, how can I shun those ideas which I have helped in strengthening myself and aided its cause for the past thirty years, on the basis of a dream?”

He said: “If I did not know that Allāh will aid you [in this], I would not have come here to explain all this. Do not make light of this dream in which I have come. Is that in which I saw Gibrīl, just another dream? I will not come again to you. Do well and Allāh will aid you.”

I woke up and said to myself: only falsehood remains after truth has been manifest. So I began to advocate ĥadīth about seeing Allāh, intercession etc. And I have found proofs – by Allāh – which I have never heard before, nor read in a book. This, I have realized to be the aid from Allāh, the good news of which was given to me by RasūlAllāh şallAllāhu álayhi wa sallam.

Tabyīn, pg. 51/52