The Prophet (ﷺ) wiped his head with water which was left over in his hand.
Sunan Abi Dawud Book 1, Hadith 130
← Previous Hadith I saw the Messenger of Allah (ﷺ) performing ablution. He wiped his head front and back, his temples and his ears once.

Sunan Abi Dawud Book 1, Hadith 129 Next Hadith → The Prophet (ﷺ) performed ablution. He inserted his two fingers in the ear-holes.

Sunan Abi Dawud Book 1, Hadith 131