Al-Tabari's account is different. He says that Kavad's sister helped him to escape by rolling him in a carpet, which she made the guard believe was soaked with her menstrual blood. The guard did not object or investigate the carpet, "fearing lest he become polluted by it." One of the authors of the "Prosopography of the Later Roman Empire", John Robert Martindale, proposes she may have in fact been Sambice, Kavad's sister-wife, who was the mother of his eldest son, Kawus. Regardless, Kavad managed to escape imprisonment, and fled to the court of the Hephthalite king, where he took refuge. According to the narratives included in the history of al-Tabari, during his flight Kavad met a peasant girl from Nishapur, named Niwandukht, who became pregnant with his child, who would later be Khosrow I. However, the story has been dismissed as "fable" by the Iranologist Ehsan Yarshater. Khosrow's mother was in reality a noblewoman from the Ispahbudhan clan, one of the Seven Great Houses of Iran. At the Hephthalite court, Kavad gained the support of the Hephthalite king, and also married his daughter (who was Kavad's niece).