Sayyidah Aishah Siddiqah (may Allah be pleased with her) narrates that she was obliged to free a slave from the descendants of Sayyiduna Isma'il (peace be upon him). Some captives from the Khawlan tribe came from Yemen, and Sayyidah Aishah (may Allah be pleased with her) intended to free one of them, but the Prophet (peace and blessings be upon him) forbade her. Then some captives of Banu al-Anbar, of the Mudar tribe, came, and the Prophet (peace and blessings be upon him) instructed Sayyidah Aishah (may Allah be pleased with her) to free one of them.
Ahmad recorded it, and its chain contains a narrator whom I do not know. Other hadiths of this kind will come in the chapter on virtues (Manaqib).
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب العتق / 7251