Yahya related to me from Malik that he had heard that Abdullahibn Abbas and Abdullah ibn Umar were asked about a man who had a freewoman as a wife and then wanted to marry a slave-girl. Theydisapproved that he should combine the two of them.
USC-MSA web (English) reference: Book 28, Hadith 28
Arabic reference: Book 28, Hadith 1122