It is narrated from the Mother of the Believers, Sayyidah Juwayriyah (may Allah be pleased with her), that she said: "O Prophet of Allah, I intend to free this slave."
So the Messenger of Allah (peace and blessings be upon him) said: "Rather, give him to one of your maternal aunts who live among the Bedouins, so that he may graze their livestock, for that will bring you a greater reward."
Hadith Referenceالمعجم الأوسط / باب الألف / 975
Hadith Takhrij«أخرجه النسائي فى «السنن الكبرى» برقم: 4914»