Is it permissible to supplicate against someone who has shown me enmity and wronged me unjustly, knowing that I have forgiven him, yet he persists in shunning me? And is there a specific supplication for repelling injustice?

Islam is keen on fostering affection and harmony among Muslims, especially relatives. If your sister's husband has indeed insulted you and treated you with hostility without cause, he has done wrong. You have done well by forgiving him, as Allah Almighty says: "And those who pardon people," and the Prophet, peace and blessings be upon him, said: "Allah increases a servant in nothing but honor by his forgiveness." It is not permissible for him to prevent you from speaking to him or greeting him, as this is an unjustified call for abandonment according to Islamic law. We advise you to be patient, strive for reconciliation, and seek the reason for his anger. There is no harm in seeking assistance from someone who can mediate between you. supplicating against an oppressor is permissible, but forgiveness is better. It is not permissible for you to sever ties with your sister without a valid شرعي excuse, as cutting off family ties is forbidden and a major sin.