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." (IT)
USC-MSA web (English) reference: Book 30, Hadith 4 (IT)
Arabic reference (IT): Book 30, Hadith 1278 (IT)