Do not be sad: Seek forgiveness from Allah often, for your lord is Oft-Forgiving

(I [Noah] said [to them]: ‘Ask forgiveness from your Lord; verily, He is Oft-Forgiving. He will send rain to you in abundance; and give you increase in wealth and children; and bestow on you gardens; and bestow on you rivers.) (Qur’an 71: 10-12)

So seek forgiveness from Allah more often and you will reap the benefits of doing so: peace of mind, lawful provisions, righteous off-springs, and plentiful rain.

(And [commanding you]: ‘Seek the forgiveness of your lord, and turn to Him in repentance, that He may grant you good enjoyment, for a term appointed. And that He may bestow His abounding Grace to every owner of grace [i.e. the one who helps and serves the needy and deserving, physically and with his wealth, and even with good words].) (Qur’an 11:3)

And the Prophet (Blessing and peace be upon him said:

“Whosoever seeks forgiveness (from Allah) often, then Allah makes for him a good ending for every matter of concern and provides for him a way out of every situation.”

Related in Bukhari is a hadith that is known as the chief of Al-Istighfaar (i.e. of supplications with which one asks Allah for forgiveness):

“O’ Allah, You are my Lord and none has the right to be worshiped except you. You have created me and I am your slave; and I am upon your covenant and promise as much as I am able to be. I seek refuge in You from the evil that I have perpetrated. I confess to You Your favor upon me, and I confess to You my sin, so forgive me; for verily, none forgives sins except You.”