الادهان وترجيل الشعر
Regular application of oil to the hair and scalp as part of routine grooming, mentioned approvingly and contrasted with a neglected, disheveled appearance.
مَنْ كَانَ لَهُ شَعْرٌ فَلْيُكْرِمْهُ
“Whoever has hair should take care of it [with oil and grooming].” (meaning, not a literal translation)
A man came before the Prophet ﷺ with disheveled hair and he gestured that he should go and fix it (Muwatta Malik).
Ibn al-Qayyim discusses hair oils as protecting against dryness and brittleness, within the same category as olive oil's benefit for skin.