Musnad Abu Ya'la al-Mawsili 217:20

Zuhayr narrated to us, al-Hasan ibn Musa narrated to us, Ibn Lahi'ah narrated to us, Bukayr ibn al-Ashajj narrated to us, from Kurayb, the freed slave of Ibn Abbas, who said: I heard Maymunah say: I emancipated a slave girl during the time of the Messenger of Allah, may Allah bless him and grant him peace. I mentioned that to him, and the Messenger of Allah, may Allah bless him and grant him peace, said to me: "If you had given her to your maternal uncles, it would have been greater for your reward."