Is it permissible to supplicate at the grave of the Prophet (peace be upon him) with the words: "May Allah destroy the oppressor, the liar, and the instigator of discord," concerning the accusations of the husband's family regarding their breaking up the family, and how should one deal with them and with the husband?

There is no harm in supplicating against an oppressor, though patience and saying "Allah is sufficient for us, and how excellent a guardian He is" is more preferable, for whoever has Allah as his sufficiency, He will suffice him. Supplication is prohibited at the graves of prophets and righteous people. We advise patience and repaying evil with good, and be an aid to your husband, not an adversary to his family.