The Prophet ﷺ used to anoint his head with oil while in the state of ihram, provided it was not perfumed oil.
حدثنا علي بن محمد حدثنا وكيع حدثنا حماد بن سلمة عن فرقد السبخي عن سعيد بن جبير
أن النبي ﷺ كان يدهن رأسه بالزيت وهو محرم غير المقتت
Its chain of transmission is daif. Tirmidhi narrated it in the chapter on Hajj, in the section on the muhrim applying olive oil, hadith 962, from the hadith of Waki, with the same wording, and he said, "Gharib..." Farqad's status was mentioned earlier, hadith 1781. Bukhari also narrated it, 1537, from Ibn Umar, similarly but abridged, as a mawquf report.