Read it here on my blog https://bit.ly/3hwaK5N
The concept of nikah halala
Islam dictates that a Muslim man has the liberty to divorce and re-marry the same woman twice.
A man can legally divorce his wife by simply pronouncing talaq (the Arabic word for divorce). He can do that three times. After the first and second talaq, the husband can still re-marry her, but after the pronouncement of the third talaq, the woman becomes ‘haram’ (unlawful and therefore, prohibited) for the husband and he can't re-marry her.
However, if the husband and wife want to re-marry for the third time, it can be done only on one condition: the woman has to marry another man and sleep with him (nikah halala)
Only, if the second husband divorces her after sexual intercourse or dies, the woman after completing the Iddat period, can re-marry the first husband. In case the second husband dies or divorces her before sexual intercourse, then it will be of no account and she can't marry the first husband in such condition.