Question text What is the meaning of the number "40" in the Quran? Why 40? Why not 39 or any other number?
categorization: Qur’anic Sciences
Answer
The number of 40 is not the only number mentioned in the Qur'an. Other numbers seven, twelve, nineteen, twenty, thirty, etc. The number 40 is only mentioned in the Qur'an on three occasions, and this was only to describe certain historical events. The number 40 does not have particularly significance as opposed to any other number. Nonetheless, there are some narrations which focus on the number 40, such as praying for 40 believers in one's night prayer, or memorizing 40 hadith. Nonetheless, we do not know the number 40 with regards to these narrations, but Allah knows best.

resources
Ref: www.islamichouseofwisdom.com