Is the following Hadith authentic: "A man came to the Messenger and embraced Islam, then said to the Messenger Muhammad, peace and blessings be upon him, 'I cannot abandon fornication,' so he said to him, 'Pray and commit fornication'?"

There is no hadith (definition) with this meaning that permits adultery, rather it contradicts the agreed-upon principles of Islam concerning the prohibition of adultery. A sound hadith has been narrated on the authority of Abu Umamah in which the Prophet, peace and blessings be upon him, rejected a young man's request for permission to commit adultery, explaining to him the ugliness of adultery by stating his disinclination for it to befall his mother, daughter, sister, paternal aunt, or maternal aunt. He then prayed for him to repent and remain chaste.