Yahya related to me from Malik from Ibn Shihab from Amr ibn ash-Sharid that Abdullah ibn Abbas was asked whether, if a man had twowives, and one of them nursed a slave-boy, and the other had nursed aslave-girl, could the slave-boy marry the slave-girl. He said, "No.The husband is the same."
USC-MSA web (English) reference: Book 30, Hadith 5
Arabic reference: Book 30, Hadith 1279