Musnad Ahmad 32:1562

Hassan ibn Musa narrated to us, Hammad ibn Zayd narrated to us, from Shu'ayb ibn al-Habhab, and 'Abd al-'Aziz ibn Suhayb, and Thabit al-Bunani, from Anas ibn Malik: "That the Messenger of Allah, peace and blessings of Allah be upon him, emancipated Safiyyah and made her emancipation her dowry."