Al-Baqarah 2:230 فان طلقها فلا تحل له من بعد حتى تنكح زوجا غيره فان طلقها فلا جناح عليهما ان يتراجعا ان ظنا ان يقيما حدود الله وتلك حدود الله يبينها لقوم يعلمون ٢٣٠

And if he has divorced her [for the third time], then she is not lawful to him afterward until [after] she marries a husband other than him.¹ And if he [i.e., the latter husband] divorces her [or dies], there is no blame upon them [i.e., the woman and her former husband] for returning to each other if they think that they can keep [within] the limits of Allāh. These are the limits of Allāh, which He makes clear to a people who know [i.e.,understand].

So if a husband divorces his wife ˹three times˺, then it is not lawful for him to remarry her until after she has married another man and then is divorced. Then it is permissible for them to reunite, as long as they feel they are able to maintain the limits of Allah. These are the limits set by Allah, which He makes clear for people of knowledge.