Musnad Ahmad 32:990

Isma'il ibn Ibrahim narrated to us, 'Abd al-'Aziz ibn Suhayb narrated to us, from Anas ibn Malik: "That the Messenger of Allah (peace and blessings of Allah be upon him) emancipated Safiyyah and married her." He said: Thabit said to him: "What did he give her as a dowry?" He said: "Her own self; he emancipated her and married her."