Maliks Muwatta Book 20, Hadith Number 198.

Section : Cutting the Hair.

Yahya related to me from Malik from Nafi that Abdullah ibn Umar once met a relative of his called al-Mujabbar who had done the tawaf al-ifada but, out of ignorance, had not shaved his head or cut his hair. Abdullah told him to go back and shave his head or cut his hair, and then go back and do the tawaf al-ifada.