Is there a Hadith stating that whoever consistently says the opening Takbir (Takbirat al-Ihram) for forty days during the Fajr prayer will be cleared of disbelief (kufr) and hypocrisy (nifaq)?

It is stated in (Shu'ab al-Iman by Al-Bayhaqi) a Hadith: "Whoever prays the dawn (Ghadah) and the last evening ('Isha' al-Akhirah) prayers in congregation, without missing a single rak'ah, will have two immunities written for him: an immunity from the Fire and an immunity from hypocrisy." However, this Hadith is weak and not authentic.

It is also reported in (Sunan al-Tirmidhi) with the wording: "Whoever prays to Allah for forty days in congregation, reaching the first takbir, will have two immunities written for him: an immunity from the Fire and an immunity from hypocrisy." This Hadith was weakened by Al-Tirmidhi and others due to irsāl (a break in the chain of narration), but Al-Albani and some later scholars considered it hasan (good).

The Hadith is not limited to the Fajr prayer; rather, the reward in it is linked to maintaining the takbirat al-ihram (opening takbir) in all five prayers. Despite the possibility of its authenticity, it is hoped that whoever strives to act upon it will attain this virtue, and the least they will achieve from that is accustoming themselves to maintaining the ritual of prayer.