What is the ruling on insidious doubt concerning one's wife?

A righteous wife is a source of happiness, and a bad one is a source of misery. The Prophet, peace and blessings be upon him, said: "Three things bring happiness to the son of Adam... a righteous wife... And three things bring misery to the son of Adam... a bad wife." And he, peace and blessings be upon him, also said: "Beware of suspicion, for suspicion is the falsest of speech." Sufyan said: "Suspicion is of two kinds: suspicion that is a sin, and suspicion that is not a sin." Jabir ibn Atik reported that the Messenger of Allah, peace and blessings be upon him, said: "Indeed, some jealousy is loved by Allah, the Mighty and Majestic, and some He hates. As for the jealousy that Allah loves, it is jealousy in the case of suspicion (or doubt). And the jealousy that Allah hates is jealousy in a case without suspicion (or doubt)."

Therefore, do not rush to judge your wife. If she is righteous, then praise be to Allah. If you find strong evidence to the contrary, then advise her and remind her of Allah. If she returns (to righteousness), then praise be to Allah. Otherwise, you have the option to separate from her if you wish, or to remain with her as long as no reprehensible act has been confirmed. Mere suspicion is not acted upon.