WHY 40 SALAAT IN MASJID NABAWI

The author of Majma Uz Zawaaid, Hadhrat Ali Bin Abu Bakr Bin Sulaiman Haithami (May Allah shower His Mercy on him) writes after mentioning this Hadith:

Translation: I say that Imam Tirmidhi has recorded a part of this Hadith. Imam Ahmed has recorded this in his Musnad and Imam Tabarani in his Mo’jam Ausat and the persons who narrate this Hadith are reliable and trustworthy.

This Hadith is also mentioned in
(Mo’jam Ausat of Imam Tabarani, Vol. 5), with a slight change in wording:

Translation of Hadith: It has been narrated on the authority of Hadhrat Anas (May Allah be well pleased with him) that the Holy Prophet (Sallallahu alaihi wa sallam) said: Whoever offers 40 Salaat in My Masjid in such a way that no Salaat is missed, Allah (Subhanahu wa Ta’ala) decrees for that person freedom from Hell and deliverance from the punishment of Hell.