Is a Muslim obligated to conceal the secret of marital infidelity committed by a married neighbor with her husband's friend?

Adultery is a grave evil. Whoever becomes aware of it must denounce it according to their ability, without accusing someone of it (qadhf). For whoever accuses chaste women without four witnesses shall be flogged eighty lashes, and their testimony shall never be accepted, as Allah the Almighty says: "And those who accuse chaste women and then do not produce four witnesses - flog them eighty lashes and never accept their testimony. And those are the defiantly disobedient, except for those who repent thereafter and reform, for indeed, Allah is Forgiving and Merciful." It is necessary to advise the neighbor and threaten her with informing her husband if she persists. The advice can be direct or through a message. If she responds, then conceal the matter. If she does not respond, then inform her husband without accusing her directly (qadhf), by saying: "Watch over your family," or "Others enter upon your family," or "They meet with others," and it is preferable for this message to be anonymous. Silence on this evil is not permissible.