Is it unlawful for a man to marry a woman with the intention of making her lawful for her first husband after the marriage contract is concluded and consummated, and then divorcing her?

A severe warning has been established regarding marriage to a thrice-divorced woman with the intention of making her lawful for her former husband, as the Prophet, peace and blessings be upon him, said: "Allah has cursed the one who makes a woman lawful (for her former husband) and the one for whom she is made lawful." This prohibition is specific to explicitly stating the condition of making her lawful or intending it at the time of the marriage contract. However, if a man marries a woman out of desire, and then the intention of making her lawful for her former husband occurs to him, she becomes lawful for her former husband, and he incurs no sin thereby. Al-San'ani mentioned forms of prohibited 'tahlil' (making lawful), such as stipulating 'tahlil' in the contract or secretly intending it and colluding upon it. Al-Adawi mentioned that the decisive factor is the intention at the time of the contract, and a subsequent intention of 'tahlil' at the time of intercourse does not cause harm.