40 Astaghfar - چہل استغفار

The virtue of Astaghfar | Astaghfirullah | Seeking Forgiveness:
Astaghfirullah is the simple but very important powerful Dua. Astaghfar is expressing that remorse and cry for the forgiveness of Allah. Astaghfar is the keyword to changing the destination from hell to heaven. So it is super protection from the devil and a way to get to the vicinity of the almighty Allah. Repentance [Tawbah] and Istighfar is the most meritorious acts for the Muslims. It is a simple but powerful supplication. Seeking forgiveness of Allah 100 times a day is Sunnah of beloved Prophet Muhammad (ﷺ). Tawbah is not only necessary for seeking the shelter of sin but it is also the thankfulness of Allah for his immense favour to us. As we realize the greatness of Allah, Most High, our efforts of obedience clearly are seen to be Inadequate. But a person higher on the scale of taqwa and do more Astsghfar consequently get the mercy of Allah.

ISTIGHFAR | IMPORTANCE IN THE QURAN

One of the great names of Allah is Al-Ghaffar which meaning is The Great Forgiver The Forgiver. So Allah is one who forgives the sinner one time and also again. There is a number of verses in the Quran about the importance of Astaghfar. A few of them are as under:

And seek your Allah,s forgiveness and turn toward Him in repentance. He will grant you a good provision for an arranged term and graciously reward the doers of right. But if you move away, then I truly fear for you the torment of a formidable Day.
Hud 11:3

Then, verily! Your Lord for those who do evil (commit sins and are disobedient to Allâh) in ignorance and afterwards repent and do righteous deeds, verily, your Lord thereafter, (to such) is Oft-Forgiving, Most Merciful.
An-Nahl 16:119

But indeed, I am the Perpetual Forgiver of whoever repents and believes and does righteousness and then continues in guidance.
Ta-Ha 20:82

And say (O Muhammad (ﷺ)): “My Lord! Forgive and have mercy, for You are the Best of those who show mercy!
Al-Mumenoon 23:118

Your Lord is most knowing of what is within yourselves. If you should be righteous [in intention] – then indeed He is ever, to the often returning [to Him], Forgiving.
Al-Isra 17:25

[O Muhammad (ﷺ)], inform My servants that it is I who am the Forgiving, the Merciful
Al-Hijr 15:49

Moreover, if you want more verses then Read the Quran. There are plenty of ayahs about the necessity of seeking the forgiveness of Allah. Some of them are addressing the previous Prophets and their nations. But these are also for addressing us as Allah wants us to learn from the stories of the previous nation., His acceptance of Astaghfar and His punishments for ignoring it.
Different Benefits of Seeking Forgiveness

Let us see the more benefits and virtues of reciting this simple beautiful supplication inShaAllah.
Cleanup of Sins

Astagfar is the way by which one can clean sin from his books of deeds. Seeking protection from evils makes a person safe. Entrance in Jannah is only possible when a person admits his sins and seek the forgiveness of Allah. A Muslim can cleanup his sins in different ways but for major sins proper Astagfar is necessary.
Astaghfar is a way of Relief and Happiness

Our ignorance of the Order of Almighty Allah brings tensions and stresses. if anyone recites Astagfar regularly, he can serve a relax life and can get rid of anxiety. I will bring peace and happiness in your life. Abdullah Bin Abas narrates that Prophet Muhammad (ﷺ) said:

The one who (regularly) says Istighfaar, that is, frequently repent to Allah Ta’aala for sins committed, Allah Azza Wa-Jal will open a path from poverty and difficulties. All sorrow and hardship will be removed, and in its place prosperity and contentment granted. One will receive sustenance from unimagined and unexpected sources.

Astaghfar Increase Sustenance