When a certain amount of research finally yields a theory, academia dictates that this theory must face rigorous testing. If it fails then it must be either modified and retested, or abandoned altogether.
But studies of Islaam [done by non-Muslims] are unfortunately littered with ill-conceived theories that have ascended to the point of almost becoming hard facts, even when they fail on several counts.
[For example] Professor Wensinck comments on the famous hadeeth regarding the five pillars of Islaam:
“Islaam has been built on five pillars: testifying there is no god but Allaah, performing the prayers, paying the zakaah, fasting Ramadhaan, and making the pilgrimage to the House (Ka’bah).” [Saheeh Muslim]
He views this as spurious since it contains the kaimah shahaadah (bearing testimony that there is no god but Allaah). According to his view, the Companions of the Prophet Muhammad introduced the kalimah only after coming across some Christians in Syria who employed a declaration of faith, this thieving this idea from the Christians to develop one of the core pillars of Islaam.
Confronted with the problem that the kalimah shahaadah is also part of the tashahhud in the daily prayers, Wensinck put forward another theory instead of modifying his earlier one: the prayer was standardised after the Prophet’s death [see Wensinck, Muslim Creed, p. 19-32].
Perhaps a further theory is required, since Wensinck has not explained the existence of the kalimah in the adhaan and the iqaamah, nor when these two were introduced into Islaam.
[“The History of The Quranic Text”, by M. M. Al-Azami, see preface p. xix]