What is the status of a Muslim female slave (jariyah) seized by a non-Muslim belligerent who subsequently engages in sexual relations with her (istawlada) and then converts to Islam?

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If a non-Muslim belligerent seizes a Muslim female slave, engages in relations with her, and subsequently converts to Islam, she becomes his property, and she is considered an Umm Walad (mother of his child) to him. Ahmad explicitly stated this ruling because she is considered property, which is analogous to all other forms of property.