Yahya related to me from Malik from Nafi from 'Abdullah ibn 'Umarthat Umar ibn al-Khattab said, "Someone who puts plaits in his hairshould shave his head, and do not plait your hair in such a way thatit seems you have matted it."
USC-MSA web (English) reference: Book 20, Hadith 200
Arabic reference: Book 20, Hadith 899