How can one respond to a person who claims to be a Muslim, but wears a cross and believes in the Qur’an while not believing in the Prophetic Hadith, and what is the convincing method for introducing the Prophetic Hadith and the Messenger Muhammad, may God’s prayers and peace be upon him?

Indeed, the denial of the Prophetic Sunnah is one of the greatest deviations. Its authoritative status, exalted position, and Allah's preservation of it have been previously clarified. Extreme caution must be exercised when discussing with those who hold deviant ideas and corrupt opinions. One must be armed with absolute certainty and sufficient religious knowledge, because engaging in debate without certainty and knowledge can cause severe harm to one's faith, for the heart is weak and doubts are insidious. Therefore, one should avoid listening to the deviants and refrain from arguing with them, except for those who possess deep-rooted knowledge. It suffices to refer them to books and fatwas.