What is the degree of authenticity of the hadith about forty prayers in the Prophet's Mosque and its consequences of immunity from hypocrisy and salvation from hellfire, and can it be used as a basis for argument despite the existing disagreement regarding its authentication and weakening?

The hadith (definition) is weak due to the anonymity of one of its narrators (Nubayt). Imam Ahmad and Al-Tabarani narrated it with the wording: "Whoever prays forty prayers in my mosque, missing no prayer, will have written for him a salvation from the Fire and a deliverance from punishment, and he will be cleared of hypocrisy." Scholars have differed regarding the authentication of Nubayt, but it appears that he is only weak.