What is the ruling of the Shari'ah regarding a man divorcing his wife after discovering she had a previous relationship, despite her denial of it before marriage?

A husband's questioning his wife about her past and the forbidden acts she committed is not permissible, and she is not obligated to answer. A person who has committed a sin should conceal himself. Divorcing a wife for these reasons is makrooh (disliked), and it may be haraam (forbidden) according to some scholars, because it causes harm without necessity, and divorce without necessity is makrooh.