What is the response to one who denies authentic Hadith, such as Sahih al-Bukhari? Is it better to argue with him or leave him? And is it permissible to interact with him?

If a man denies the Ahadith of Al-Bukhari due to his perception of their lack of authenticity, he should be responded to by convincing him of the authenticity of what Al-Bukhari definitively asserted, because scholars have agreed that the two most authentic books after the Qur'an are the two Sahih collections.

However, if he denies a Hadith of the Prophet, peace be upon him, even if its chain of transmission is sound, he should be shown the obligation of obeying him and the danger of rejecting his command and disbelieving him, based on the Almighty's saying: "And whatever the Messenger gives you, take it; and whatever he forbids you from, refrain from it," and "Whoever obeys the Messenger has obeyed Allah."

And argue with him in the best way if you possess knowledge, based on the Almighty's saying: "Invite to the way of your Lord with wisdom and good counsel, and argue with them in the best way."

As for dealing with him in buying and selling, there is no harm in it, as long as it does not lead to a legally prohibited matter.