Musnad Ahmad 30:1417

'Affan narrated to us, Hammad narrated to us, Thabit informed us, from Abu Rafi', from Abu Hurairah, that the Messenger of Allah (peace and blessings of Allah be upon him) said: "If the slave obeys his Lord and his master, he has two rewards." He said: So when Abu Rafi' was manumitted, he wept. It was said to him: "What makes you weep?" He said: "I had two rewards, and one of them has gone."