Is what happened to the husband—his knowing of his wife's relationship with another man, without it reaching the point of adultery—considered a trial for him, for which he must be patient and seek reward from Allah, especially since she has repented and become righteous, and they have three children?

Assaulting a Muslim's honor and his wife is a great trial and a heinous act. The wife must safeguard her husband in herself, as Allah Almighty says: "So righteous women are devoutly obedient, guarding in [the husband's] absence what Allah would have them guard." If the wife repents and becomes righteous, the husband must fear Allah concerning her, fulfill his duty of guardianship, be patient and retain his wife, treat her kindly, and strive to forget the matter; for Satan is keen on separating spouses, as stated in the Hadith: "Then one of them comes and says: 'I did not leave him until I separated him from his wife.' The Prophet said: 'He (Iblis) draws him near to him and says: 'You are the best!'"