Yahya related to me from Malik from Nafi that one time Abdullahibn Umar wanted to sacrifice an animal at Madina. Nafi said, "He toldme to buy him an excellent horned ram, then to sacrifice it on the Dayof Sacrifice in the place where the people prayed." Nafi continued, "Idid so and when the ram was sacrificed, it was carried to Abdullah ibnUmar who shaved his head. He was ill, and did not attend the Id withthe people." Nafi added, "Abdullah ibn Umar used to say, 'Shaving thehead is not obligatory for someone who sacrifices an animal.' Ibn Umarwould do so however."
USC-MSA web (English) reference: Book 23, Hadith 3
Arabic reference: Book 23, Hadith 1033