Mishkat al-Masabih
Ibn ‘Abbas said that the Prophet (ﷺ) wiped his head and also the inside of his ears with his forefingers and the outside with his thumbs. Nasa’i transmitted it.
وَعَنِ ابْنِ عَبَّاسٍ أَنَّ النَّبِيَّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ مَسَحَ بِرَأْسِهِ وَأُذُنَيْهِ: بَاطِنَهُمَا بِالسَّبَّاحَتَيْنِ وَظَاهِرَهُمَا بإبهاميه) (رَوَاهُ النَّسَائِيّ)
Reference