If a man says to his wife, "You are like my mother," is that considered ẓihār requiring expiation, and does it affect the continuation of their marital relationship, especially if the statement is repeated and the couple returns to their normal life after a period?

The statement uttered after an argument with the wife is considered dhuhar, whether that was intended or not, because the context of the argument directs it towards dhuhar.

Ibn Qudamah explicitly stated that this constitutes dhuhar if said during a dispute and in anger. The Permanent Committee also stated that words uttered out of anger or threat are considered dhuhar.

Therefore, the marital bond remains valid, but expiation (kaffarah) is required before resuming conjugal relations. This expiation is the freeing of a slave. If one cannot find a slave, then fasting for two consecutive months. If one is unable to do that, then feeding sixty needy persons.