Whoever Says: Astaghfirullah (I ask Allâh for Forgiveness) Sincerely, Allâh Almighty Forgives that Person

Question :

Is it true that Allah Almighty forgives every person who says Astaghfirullah?

Answer:

If a person says Astaghfirullah with a truly sincere intention to achieve forgiveness and if the conditions of repentance are met, Allah Almighty forgives that person; indeed, Allâh Almighty loves for a person to do so:
"Truly, Allah loves those who turn unto Him in repentance and loves those who purify themselves."

The Prophet ﷺ informed us that Allâh Almighty is as pleased when one of his creatures repents, just as a man who finds his camel after he lost it while it was carrying his food and drink. He searches for it, but since he doesn't find it, he rests under a tree waiting for death to overtake him. Suddenly, he wakes to find the bridle of his camel tied to the tree. He takes the bridle and he says, "O Allâh, You are my servant, and I am Your lord."

Because of the intensity of his joy, he erred. And nobody can estimate the level of this joy except for the person who suffered similarly went through this experience.

Allâh Almighty loves that His servant repent to Him and seek His forgiveness, so He ordered us to ask forgiveness from Him in a number of verses in His book. Istaghfar or seeking forgiveness means to seek Al-Maghfirah and Al-Maghfirah means covering a sin and overlooking it. It is derived from the word Al-Mighfar, which covers a person's head during battle and protects him from arrows. So the root word combines the meanings of covering and protection. Similarly, Al-Maghfirah combines both meanings covering the sin and protecting its doer from its punishment.

Source:
Ibn 'Uthaimin
Fatawa Islamiyah, Vol. 7 Pages 239-240