Killing some people during a war with a neighboring tribe

Q: An old person told me that on the first days of the rise of the Kingdom of Saudi Arabia in this district, the chief of their tribe asked the ruler of Bishah at that time to allow him to invade Tihamah. The ruler of Bishah gave him the permission to do so. The chief summoned them and asked them to be ready to fight. There was a fight between them and the people of Tihamah. Four people were killed, but he killed a person from the people of Tihamah in that battle. When I asked him about the reason for going to such fighting, he replied that he went to fight with his tribe (Part No. 24; Page No. 365) after a request from his chief to fight the people of Tihamah and subdue them. Now, he asks about what he can do to clear himself from such guilt. Give us the ruling on this, may Allah increase you in knowledge!

A: If the reality is as you have mentioned, this person can seek Allah's forgiveness. Also, he can turn to Allah with sincere repentance and do good deeds as much as possible so that Allah may pardon him.May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.