What is the best way to tell a husband that his daughter is not his biological daughter?

The honor of Muslims is protected, and it is not permissible to violate it. A daughter is attributed to her mother's husband unless the husband denies her through li'an (oath of condemnation). The Shari'ah (Islamic law) encourages covering the faults of Muslims and forbids violating their honor. Whoever denies the lineage of a person is considered a slanderer and deserves the hadd punishment unless he brings clear proof.

The questioner has no right to inform the woman's husband of anything. Adultery with a married woman is dangerous due to its potential to corrupt the woman against her husband and to mix lineages. Its ugliness increases if it is committed by a neighbor.

A married woman should not allow anyone into her home whom her husband dislikes. The mother who committed a sin should conceal herself, repent, and seek forgiveness from her husband without explicitly disclosing what happened. It is advisable to marry her daughter to a man who will take her away from her paternal uncles, in accordance with the hadith, "The child belongs to the bed, and for the adulterer is the stone."