Question: Is it correct that I debate with a Christian using the intellect without the Book and the Sunnah?
Answer: “Yes, if the one whom he is debating with does not believe in the Book and Sunnah. He debates using the intellect.
However, it is not necessary for a person to argue except with knowledge and insight. If his debate will harm Islam and the Muslims, then he does not do that. This is only for the People of Knowledge who have insight. As for the one who does not have knowledge, then he does not do that. This is only allowed for the People of Knowledge”
[Sharh Kitab al-Imaan Abu Ubaid no. 14]
Faisal Ibn Abdul Qaadir Ibn Hassan