Nafi' (may Allah have mercy on him) said that Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) once offered a sacrifice in Madinah. Nafi' said: He ordered me to buy him a horned, uncastrated ram, and then to slaughter it on the day of Adha at the people's prayer ground. Nafi' said: I did so. Then the ram was carried to Abdullah, and he shaved his head when the ram was slaughtered; he was ill and had not attended Eid with the people. Nafi' said: Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) used to say: Shaving the head is not obligatory on one who sacrifices if he has not performed Hajj. Yet Abdullah bin Umar did it.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الضحايا / 19190