Yahya related to me from Malik from Nafi that Abdullah ibn Umarsaid, "There is no kinship by suckling except for a person who isnursed when he is small. There is no kinship by suckling over the ageof two years." (ID)
USC-MSA web (English) reference: Book 30, Hadith 6 (ID)
Arabic reference (ID): Book 30, Hadith 1280 (ID)