Musnad Ahmad 32:923

Yahya ibn Sa'id narrated to us, Hisham ibn Abi 'Abd Allah narrated to us, Shu'ayb ibn al-Habhab narrated to us, from Anas ibn Malik: "That the Messenger of Allah, peace and blessings of Allah be upon him, emancipated Safiyyah, and he made her emancipation her dowry — or her bridal gift." Yahya said: "Or he gave her her emancipation as her dowry."