Assalamualaikum

The act of wiping is obligatory and the it is from daleel Qati(a clear, unequivocal text). As far as the extent of the wiping goes that is Daleel Dhanni because there are difference of opinions on it. The hanafis say 1/4 is what is obligatory due to their understanding of the verse which makes wiping obligatory for a sound wudhu and there are ahadith from the Prophet(saw) indicating that he at times did masah on his forehead(nasiyah) which is 1/4 of the head.

This is the Quranic verse: It is Surah Maidah verse 6: "O you who have believed, when you rise to [perform] prayer, wash your faces and your forearms to the elbows and wipe over your heads and wash your feet to the ankles".

waAllahu alam.

inshaAllah we can get other input as well.