It is narrated from Sayyiduna Abdullah bin Mas'ud (may Allah be pleased with him) that Sayyidah Aishah (may Allah be pleased with her) was obliged to free a slave from the descendants of Isma'il. Then some captives of Banu al-Anbar arrived, so the Prophet (peace and blessings be upon him) ordered her to free one of them, and he said: "Whoever is obliged to free someone from the descendants of Isma'il should not free anyone from Himyar."
Ali bin Abis said: I asked Isma'il bin Abi Khalid: "Who were Himyar?" He said: "They were older (more ancient) than Isma'il (peace be upon him)."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 10362