Musnad Ahmad 32:2159

Bahz narrated to us, Hammad—meaning Ibn Salamah—narrated to us, he said: Shu'ayb ibn al-Habhab and 'Abd al-'Aziz ibn Suhayb informed 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."