Musannaf Ibn Abi Shayba 7:323

Muhammad ibn Bishr al-‘Abdi narrated to us, from Mis‘ar, from ‘Ubayd ibn al-Hasan, from Ibn Ma‘qil, who said: ‘A’ishah had an obligation of a neck or a soul to set free from the children of Ishmael. He said: Then captives arrived from Yemen. Mis‘ar said: I think he said from a tribe called Khawlan. He said: So he forbade her from setting any of them free. He said: Then captives arrived from Mudar—I think he said from Banu al-‘Anbar—so he commanded her to set some of them free.