Virtues of Doing Istighfar ( Asking Forgiveness From Allah)

'Istighfar' Or Saying 'Astaghfirullah' are Arabic words which means "I seek forgiveness of Allah". It is a very simple but an important supplication for every good Muslim to remember.
We are all human beings and we can always make mistakes but Allah, the Merciful has kept the doors for repentance open for us and if we make mistakes or commit any sin it is our duty to seek Allah's forgiveness and to repent to Him.
Also it is important to note that it is not necessary to do istighfar only if we commit a sin instead we should supplicate and seek forgiveness from Allah at all times because our acts of worship and obedience are clearly insufficient to thank Allah for all the blessings which He has given us.
Allah says in the Holy Quran in Surah Az Zumar Chapter 39 verse 53:

Say; O my servants who have transgressed against there souls, despair not of the mercy of Allah; for Allah forgives all sins; for he is Oft Forgiving, Most Merciful.

A similar message is repeated in Surah Nisa Chapter 4 verse 110:

If anyone does evil or wrongs his own soul, but afterwards seeks Allah's forgiveness, he will find Allah Oft Forgiving, Most Merciful.

Surah Najam Chapter 53 verse 32:

Those who avoid great sins and indecent deeds, only (falling into) small faults- certainly , your Lord is ample in forgiveness.....

Surah Hud Chapter 11 verse 90:

But ask forgiveness of your Lord, and turn unto Him (in repentance), for my Lord is indeed full of Mercy and loving kindness. 

Asking Allah for forgiveness and repenting on our sins will wash away our bad deeds and can even change them into good deeds. This is what Allah told in the Holy Quran in Surah Furqan Chapter 25 verses 70-71:

Except for those who repent, believe and do righteous deeds, for them Allah will change the evil into good deeds, and Allah is Oft- Forgiving, Most Merciful. And whoever repents and does good has truly turned to Allah with an (acceptable) conversion- in repentance. 

Istighfar A Means For Increase In Sustenance and Offspring:  
Seeking Allah's forgiveness and supplication with Istighfar is among the reason behind sending down of rain by Allah for the growth of vegetation and provision for animals as well as Allah blesses with good offspring and strength to those who do Istighfar.
Allah says in Surah Hud chapter 11 verse 52:

.....Ask forgiveness of your lord, and turn to Him (in repentance). He will send you the clouds pouring abundant rain and add strength to your strength, so do not turn back in sin.

A similar message is repeated in Surah Nuh Chapter 71 verse 10-12:

....Ask forgiveness from your Lord for he is Oft Forgiving. He will send rain to you in abundance. Give you increase in wealth and sons, and bestow in you gardens and bestow on you rivers (of flowing water).

Supplications From the Holy Quran And Hadith For Seeking Forgiveness:

1. Our Lord! we have indeed believed, forgive us, then our sins and save us from the agony of the fire. ( Surah Al-Imran Chapter 3 verse 16)

2. Our Lord! we have wronged our own souls, if You forgive us not and bestow not upon us Your mercy, we shall certainly be lost. ( Surah Aaraf Chapter 7 verse 23)

3. Glory be to You! to You I turn in repentance and I am the first to believe. ( Surah Aaraf Chapter 7 verse 143)

4. Glory to our Lord! surely we have been doing wrong. ( Surah Qalam Chapter 68 verse 29)

5. There is no god but You, Glory to You, I was indeed wrong. ( Surah Anbiya Chapter 21 verse 87)

6. Our Lord ! condemn us not if we forget or fall into error, our Lord! lay not on us a burden like that which You did lay on those before us, our Lord ! lay not on us a burden greater than we have strength to bear. Blot our sins, and grant us forgiveness. Have mercy on us. you are our Protector, help us aginst those who stand against faith ( Surah Baqarah Chapter 2 verse 286)

7. O Allah! You are my Lord. There is no true god except You. you have created me, and i am Your slave and i hold to Your Covenant as far as i can. i seek refuge in you from the evil of what I have done, i acknowledge the favors that You have bestowed upon me, and i confess my sins. Pardon me for none but You has the power to forgive. ( Sahih Bukhari)

8. I seek the Forgiveness of Allah and repent to Him ( Shaih Bukhari)

The above article is just a brief summary of the countless virtues of Istighfar. May Allah guide us all and forgive our sins. Ameen