Yahya related to me from Malik, from Abd ar-Rahman ibn al-Qasim,from his father, that Umar ibn al-Khattab said, "People of Makka, whyis it that people arrive dishevelled while you still have oil on yourhair? Go into ihram when you see the new moon."
USC-MSA web (English) reference: Book 20, Hadith 50
Arabic reference: Book 20, Hadith 755