Musannaf Ibn Abi Shaybah 34655 — The virtue of the Arabs

Sa'id bin al-Musayyib said that Sayyiduna Umar (may Allah be pleased with him) forbade an Arab from marrying a slave woman. And he ruled, concerning Arabs who marry slave women and their children, that there is a ransom: six qala'is (young she-camels), men and women being equal in this, and the same is the ruling for the mawali (clients) if it was not known.