Does a man's adultery with his wife's sister make his wife unlawful for him?

Allah the Almighty has forbidden combining two sisters [in marriage]. Scholars have differed on whether one who commits adultery with his wife's sister is considered as if he had married her or not.

Imam Ahmad was of the opinion that the husband should refrain from having intercourse with his wife until her sister has completed three menstrual cycles.

Some have cited two hadiths as evidence: "Whoever believes in Allah and the Last Day should not combine his semen in the womb of two sisters," and "Accursed is he who combines semen in the womb of two sisters." These two hadiths have no basis; they are fabricated.

The correct view is that adultery does not affect the unlawfulness of the wife. Rather, the woman with whom adultery was committed must observe an 'iddah (waiting period) if she wishes to marry after her repentance, and her 'iddah has no relation to the husband's intercourse with his wife.