I know those who claim Maria al-Qibtiyya(r.a) was slave believe she later became free after giving birth to prophet's(s.a) son
But my question is, was she slave before giving birth to prophet's son. Prior to Islam there were many sources of slave but after Islam only source of slave is captives captured in war or children of slaves. Maria was neither of them, she was gifted by a king and she belonged to a noble family in that place. https://ar.wikipedia.org/wiki/%D9%85%D8%A7%D8%B1%D9%8A%D8%A9_%D8%A7%D9%84%D9%82%D8%A8%D8%B7%D9%8A%D8%A9
Then why she is considered as slave ?