«وَامْسَحُوا بِرُءُوسِكُمْ»
Wipe your heads.
The verse establishes wiping the head, but a separate question asks how much is required: some portion, a specified fraction, or the whole head. A numerical limit needs its own proof.
The reported wiping of the forelock contributes to Hanafi legal analysis; the well-known Hanafi minimum is a quarter of the head. That fraction is not simply the dictionary meaning of “heads.” The source distinguishes the absolute wording from subsequent evidentiary specification.