Musnad Ahmad 788:172

Aswad ibn Amir narrated to us, Abu Bakr and Husayn ibn Muhammad informed us, they said: Abu Bakr ibn Ayyash narrated to us, from Abu Hasin, from Abu Burdah, from Abu Musa, who said: The Prophet, may Allah bless him and grant him peace, said: "If a man emancipates his slave woman, then marries her with a new dowry, he shall have two rewards."