What is the ruling on one who divorced his wife and then had intercourse with her, and then it became clear to him that his divorce had not originally occurred according to one of the schools of Islamic jurisprudence?

If a man divorces his wife with a revocable divorce and has intercourse with her during her waiting period (iddah), she returns to his marital bond. It is obligatory for the layperson to seek the fatwa of scholars regarding matters, as Allah Almighty says: "So ask the people of the message if you do not know." If the muftis differ, then if the layperson comprehends the proofs, he must take the preponderant opinion. If his understanding falls short, he may imitate the most knowledgeable or follow the opinion of any of the muftis he wishes. And whoever acts upon a saying then it becomes clear to him that the truth lies elsewhere, he should act according to the new (opinion) in what is to come. There is a difference of opinion regarding his returning to the new saying concerning what he had already done based on the first saying.