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