Musnad Abu Ya'la al-Mawsili 145:6

Abu Yusuf al-Jizi narrated to us, Abdullah ibn al-Walid narrated to us, Sufyan narrated to us, from Yunus ibn Ubayd, from Shu'ayb ibn al-Habhab, from Anas: That the Prophet, peace and blessings of Allah be upon him, emancipated Safiyyah and made her emancipation her dowry.