Istighfar

And whoever does a wrong or wrongs himself but then seeks forgiveness of Allah will find Allah Forgiving and Merciful

And [saying], "Seek forgiveness of your Lord and repent to Him, [and] He will let you enjoy a good provision for a specified term and give every doer of favor his favor. But if you turn away, then indeed, I fear for you the punishment of a great Day

And said, 'Ask forgiveness of your Lord. Indeed, He is ever a Perpetual Forgiver

Al-Agharr al-Muzani, who was one amongst the Companions (of the Holy Prophet) reported that Allah's Messenger (ﷺ) said:There is (at times) some sort of shade upon my heart, and I seek forgiveness from Allah a hundred times a day

Narrated Shaddad bin 'Aus:The Prophet (ﷺ) said, "The most superior way of asking for forgiveness from Allah is: 'Allahumma anta Rabbi la ilaha illa anta. Khalaqtani wa ana `Abduka, wa ana 'ala 'ahdika wa Wa'dika mastata'tu abu'u Laka bi ni 'matika wa abu'u Laka bidhanbi; faghfirli fa'innahu la yaghfiru-dh-dhunuba ill a ant a. A'uidhu bika min sharri ma sana'tu.' If somebody recites this invocation during the night, and if he should die then, he will go to Paradise (or he will be from the people of Paradise). And if he recites it in the morning, and if he should die on the same day, he will have the same fate