Musannaf Ibn Abi Shayba 9:187

Abu Bakr narrated to us, he said: Abu Khalid al-Ahmar narrated to us, from Hajjaj, from al-Minhal, from Zirr, from Ali, who said: "If he marries a free woman alongside a slave woman, he shall divide [the time] for this one day, and for this one two days."