What is the ruling regarding fulfilling a self-imposed condition by the wife in the case of dual *mahr* stipulations (secret and public)?

Primary text

If the obligatory *mahr* is determined to be the one established publicly, it is recommended (*mustahabb*) for the wife to fulfill what she promised the husband and stipulated upon herself—that she would only take the secret *mahr*. This recommendation stems from the necessity to avoid deception and because the Prophet, peace be upon him, said, 'Muslims are bound by their conditions.'