If, for any reason, you have information that someone is at risk of being physically hurt by someone else, then you have a responsibility to take action.
If you feel that the person may be in immediate danger, contact an emergency service. You may feel you need to do this anonymously. If so, it is still better to report it, than not at all.
If you feel the person is not in immediate danger and you are working for an organisation, report your concerns to your manager so they can decide what needs to be done.
If you feel the person is not in immediate danger, and you are not working for an organisation, seek further advice from a professional agency, such as a charity caring for people suffering domestic violence.