Is the claim of a captive that he was a Muslim to be accepted?

Primary text

The claim of a captive that he was a Muslim is not accepted unless supported by two witnesses, because he claims a status contrary to the apparent situation, which affects the removal of an obligation resting upon him. If one witness testifies for him, that witness swears alongside him, and the captive is released. The basis for accepting one witness is the narration from Abdullah ibn Mas'ud that on the Day of Badr, the Prophet, peace be upon him, decreed that none of the Quraysh captives should remain except those redeemed or beheaded. When Abdullah ibn Mas'ud mentioned Suhayl ibn Bayda' as one he heard professing Islam, the Prophet, peace be upon him, confirmed, 'Except for Suhayl ibn Bayda', thus accepting Abdullah's solitary testimony.