Who was the first to say that Ahad (single-chain) narrations are not authoritative in matters of creed, and what is the easiest way to refute this belief?

Abundant evidence from the Qur'an, the Sunnah, the consensus of the Companions, and the predecessors of the Ummah confirms the obligation of accepting Ahad حديث الآحاد (single-narrator) hadith in all areas of Sharia, whether in matters of belief or practice. Differentiating between them is an innovation introduced by people of whims. The Companions, the Tabi'un (successors), and the people of Sunnah and Hadith have used these reports as evidence in matters of belief and rulings. Imam Al-Shafi'i, Ibn Abd al-Barr, and Ibn al-Qayyim affirm the consensus of Muslims on accepting single-narrator reports in beliefs and rulings. Furthermore, the claim that Ahad hadith cannot establish عقيدة (belief) is a statement that requires proof, and rejecting it leads to rejecting the entire Sunnah.