Yahya related to me from Malik from Thawr ibn Zayd ad-Dili thatAbdullah ibn Abbas said, "The milk which a child under two years oldsucks, even if it is only one suck, makes the foster relatives haram." (JA)
USC-MSA web (English) reference: Book 30, Hadith 4 (JA)
Arabic reference (JA): Book 30, Hadith 1278 (JA)