Is it permissible to take revenge on the unjust killers of one's father, who have not regretted their deed, or should the matter be surrendered to Allah Almighty?

The ruling for intentional and unjust killing is legal retribution (Qisas). The application of Sharia (definition) rulings ensures the stability of societies, as Allah Almighty says: "And there is for you in legal retribution [saving of] life, O you [people] of understanding, that you may become righteous." The implementation of rulings is entrusted to the ruler (Wali al-Amr); it is not permissible for the general public to carry it out to avoid chaos. It is advised to fear Allah, be patient, and not seek revenge, for Allah will take vengeance on the oppressor.