Yahya related to me from Malik from Nafi that Abdullah ibn Umarused to say, about sacrificial animals, "Six-year-old camels, three-year-old cows and sheep, or older than these." (RU)
USC-MSA web (English) reference: Book 20, Hadith 151 (RU)
Arabic reference (RU): Book 20, Hadith 854 (RU)