Praise be to Allah.
Shaykh Ibn ‘Uthaymeen (may Allaah have mercy on him) was asked about the ruling on taking hair from the back of the head and transplanting it in the affected spot. He said: Yes, that is permissible, because it comes under the heading of restoring that which Allaah has created, and of correcting a fault. It does not come under the heading of cosmetic procedures or adding to that which Allaah has created, or changing the creation of Allaah. Rather it is restoring something that is missing and correcting a fault. It is well known in the story of the three men, one of whom was bald and said that he wished that Allaah would give him back his hair, that the angel touched his head and Allaah gave him back his hair, and gave him beautiful hair. Al-Bukhaari, 3464; Muslim, 2964.