What is the ruling regarding a wife who is suspected of committing adultery because the bedroom door was open and a cousin was in the house, and what is the correct action to take towards her?

The wife must not be left alone with the husband's cousin, as this constitutes an unlawful seclusion (khalwa). The Prophet, peace and blessings be upon him, warned against entering upon women and clarified that the in-law (al-hamu) and those in a similar position, such as the cousin, are "death." Suspicion is not permissible in Islam, as Allah the Almighty says: "O you who have believed, avoid much [negative] assumption. Indeed, some assumption is sin." [Al-Hujurat:12], and the Prophet, peace and blessings be upon him, said: "Beware of suspicion, for suspicion is the most mendacious of speech." The crime of adultery is only proven by four witnesses, and mere doubt or suspicion is never permissible for a Muslim. The husband must not allow anyone other than her mahram (unmarriageable kin) to be secluded with his wife, and he must abandon suspicions that are not based on valid evidence. He should hold onto his wife as long as he only harbors mere suspicions or delusions.