Sahih Muslim
The Book of Zakat (Kitab Al-Zakat)
Book Number: 005 / Hadith Number: 2187
Maimuna bint Harith reported that she set free a slave-girl during the lifetime of the Messenger of Allah (may peace be upon him) and she made a mention of that to the Messenger of Allah (may peace be upon him) and he said: Had you gives her to your maternal uncles, you would have a greater reward.