Nāfiʿ reports:

ʿAbdullāh b. ʿUmar once sacrificed an uḍḥiyah in Al-Madīnah. He told me to buy a horned ram for him, and then to slaughter it on the Day of Aḍḥā at the people’s prayer place (muṣallā), so I did that. Then it was taken to ʿAbdullāh b. ʿUmar, and he shaved his head once the ram was slaughtered. He was ill at the time and had not witnessed the ʿEid with the people.

Nāfiʿ said:

And ʿAbdullāh b. ʿUmar used to say: “Shaving the head is not obligatory upon the one who sacrifices an uḍḥiyah.” But Ibn ʿUmar had himself done it.

Al-Imām Mālik, Al-Muwaṭṭā, Book of Sacrificial Slaughters, Chapter on What is Recommended of the Sacrifices.