Explanation

The Prophet (may Allah's peace and blessings be upon him) warned against mixing with foreign women and said: Guard yourselves against entering upon women and against women entering upon you. A man from the Ansār said: What about the husband's relatives, like the husband's brother, his brother's son, his uncle, his cousin, his sister's son, and others whom she could get married to if she were not married? Thereupon, the Prophet (may Allah's peace and blessings be upon him) said: Beware of him as you beware of death. This is because meeting the husband's male relatives in seclusion leads to temptation and destruction in one's religion. In fact, the husband's relatives, other than his fathers and sons, are worthier of the prohibition than the foreign man since being in seclusion with the husband's relative is more recurrent than with others, and evil is more expected from him than from others, and temptation is more likely to occur given his ability to reach the woman and stay in seclusion with her without being blamed for that, and given that his presence is inevitable and it is not possible to keep him away from her as this is commonly taken lightly, so a man can easily meet his brother's wife in seclusion. This is similar to death in terms of hideousness and the evil consequences, unlike the foreign man who is usually avoided.