A Layman’s Triple Divorce in Successive Pronouncements

Some scholars answered: it is obligatory to inquire of the layman and ask what he intended at the time of pronouncement; he is then given a fatwa according to what he intended, and his intention counts as his “madhhab.” End.
We say: This answer issued from some scholars on the basis of the established rule that what the layman does while believing it valid is valid. Therefore, they made the pure layman like an absolute mujtahid, and his madhhab is the madhhab of whomever he accords with; hence they answered as above.
What appears to me—and Allah knows best—is that the layman is left upon what he believed and is judged valid for him so long as he has not asked. If he asks about the ruling of what he did, he is not to be given a fatwa based on what he believes; rather, he must be given a fatwa according to the muftī’s madhhab—whereupon it is obligatory upon the layman to act in accordance with the fatwa. The proof for what we have said is His—Exalted is He—saying: "So ask the people of the reminder if you do not know." [Al-Anbiyāʾ:7].
Thus, if the pure layman divorced his wife three times while believing that to have taken effect and been valid, it is not permissible for him to marry her nor to take her back. If he asks and learns that only one revocable divorce has taken effect, then at that point he may take her back or marry her.
What is not intended—as it appears to me—is that the layman is like an absolute mujtahid in every respect; rather, he is so before asking. As for after asking, it is incumbent upon him to act upon the fatwa, and it is not permissible for him thereafter to pay heed to what he had believed. Likewise, the muftī should not pay heed to what the layman had believed; for what the layman had believed was only valid on account of an excuse—namely, ignorance. When ignorance is removed, the layman has no excuse to act upon it.
Source : Min Thimār al-ʿIlm wa al-Ḥikmah vol.1