Is a father's act considered striking if he slapped his daughters once on the back of their faces to stop them from fighting in Medina? And does that affect the reward for his Umrah and his good deeds, especially since it was a moment of anger and he knows the sanctity of the place? And will his repentance be accepted?

If the father did not intend to slap the face out of displeasure, but rather as a warning, then there is no sin upon him. Not every striking of the face is forbidden, as Sarah did in astonishment. However, if he did so out of displeasure with the quarrel, he has committed something forbidden due to the hadith: "He is not of us who slaps cheeks." If it was a mistake, sincere repentance erases the sin and does not affect his good deeds or his 'Umrah.