Is it obligatory to warn against a scholar who believes that knowledge is to be taken only from the Qur'an and the Hadith, and does not consider the fatwas and sayings of previous scholars, and describes those who take them as blind followers who oppose the Sunnah, which leads him to issue fatwas that contradict the consensus of scholars?

The fundamental principle is that a Muslim should follow the Book of Allah and the Sunnah of His Messenger, and give weight to the sayings of the early scholars. A layperson must emulate them in subsidiary matters that are not explicitly stated, as these require recourse to consensus (Ijma') or analogical reasoning (Qiyas). The consensus of the Imams is a decisive proof, and their disagreement is a vast mercy. It is not permissible for a Muslim to contravene an agreed-upon consensus. And for anyone who has established a sound Sunnah or a clear, decisive verse, it is not permissible for him to deviate from it based on the words of anyone, in compliance with the Almighty's saying: {Follow what has been sent down to you from your Lord}.