وَعَنْهُ قَالَ: كَانَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسلم يُكثر دهن رَأسه وتسريحَ لحيته وَيُكْثِرُ الْقِنَاعَ كَأَنَّ ثَوْبَهُ ثَوْبُ زَيَّاتٍ. رَوَاهُ فِي شرح السّنة

He said God’s messenger often greased his head and combed his beard, and he often wore a head veil as though his garment (the explanation which seems to be preferred is that the word "garment’’ here refers to the cloth like a veil which was used to protect the turban from the grease.) were that of an olive-oil seller. It is transmitted in Sharh as sunna.