One of my friends claims that the distinction between mutawatir and ahad (individual-to-individual, isolated) hadith and historical reports was introduced by a certain "Bish bin Ghiyath". He was one of the experts of kalaam (scholastic theology). He was even considered as kafir. In other words, the source of the mutawaatir vs. ahaad distinction was people of bid'ah (innovation). It has been claimed that Imam Thahabi held this in Siyar A'lam Al-Nubala'. Please comment.
This view attacks a fact on the basis that it was first discovered and introduced by an innovator. Even if we take this claim to be true that the distinction was first highlighted was by a certain innovator we have to see the claim in its own right. Those who consider that tawatur is established and absolutely authentic source of historical transfer of knowledge do not base their view on that this or that innovator introduced the idea. Rather they find it absolutely and conclusively convincing. It is a fact that every rational mind understands and acknowledges.
This distinction is clear to and is acknowledged by all the people in the world working in the field of history. In Islam also all the scholars profess and acknowledge this fact.
Take any fiqh work, read any authentic treatise on usool-e ḥadīth (science of hadith criticism), consult any mutakallim and historian you would find this principle ubiquitous. From Al-Radd Alaa Siyar al-Awzai by Imam Muhammad to al-Risalah of Imam Shafi'i all would cling to this. You will also find that the distinction is not based on any religious argument but on established rational facts.