‘Whoever says:

أَسْتَغْفِرُ اللهَ الَّذِي لَا إِلَهَ إلَّا هُوَ الحَيُّ القَيّوُمُ وأَتُوبُ إِلَيهِ

‘Astaghfirullah al-Adheemal-lathee laa ‘ilaaha ‘illaa Huwal Hayyul Qayyoomu wa ‘atoobu ‘ilayhi.

‘I seek the forgiveness of Allah the Mighty, Whom there is none worthy of worship except Him, the Living, the Self-Subsisting and Supporter of all, and I turn to Him in repentance.’

Allaah will forgive him even if he was one who fled during the advance of an army.’

Abu Dawud 2/85, At-Tirmidhi 5/569
Al-Albanee Sahih t-Tirmidhi 3/182

’Ubaadah ibn as-Saamit radiallaahu ’anhu related that the Prophet sallallaahu ’alayhi wa sallam said:

“Whosoever seeks forgiveness for the believing men and the believing women, Allaah will record for that person – equivalent to every believing man and believing woman – a good deed.”

Related by al-Haythamî in Majma’az-Zuwaa‘id (l/210) where he said: “The isnaad is jayyid.”
[at-Tabarani, classed as Hasan by Al-Albani]

Supplications from the Noble Qur’aan:

[Qur’aan 59:10]

“Our Lord! Forgive us and our brethren who have preceded us in Faith, and put not in our hearts any hatred against those who have believed. Our Lord! You are indeed full of kindness, Most Merciful. (Al-Hashr 59:10)

“Rabbana ighfir lana wali ikhwanina allatheena sabaqoona bi aleemani wala tajal fee quloobina ghillan lillatheena amanoo rabbana innaka raoofun raheemun

رَبَّنَا اغْفِرْ لَنَا وَلِإِخْوَانِنَا الَّذِينَ سَبَقُونَا بِالْإِيمَانِ وَلَا تَجْعَلْ فِي قُلُوبِنَا غِلًّا لِّلَّذِينَ آمَنُوا رَبَّنَا إِنَّكَ رَؤُوفٌ رَّحِيمٌ

[Qur’aan 71:28]

“My Lord! Forgive me, and my parents, and him who enters my home as a believer, and all the believing men and women.” (Nuh 71:28)

رَبِّ اغْفِرْ لِي وَلِوَالِدَيَّ وَلِمَن دَخَلَ بَيْتِيَ مُؤْمِنًاوَلِلْمُؤْمِنِينَ وَالْمُؤْمِنَاتِ

Rabbi ighfir lee waliwalidayya waliman dakhala baytiya muminan walilmumineena wa almuminaat