Ibn Mas`ud (May Allah be pleased with him) said: The Messenger of Allah (sallallaahu ’alayhi wa sallam) said, “He who says:
`Astaghfir ullah-alladhi la ilaha illa Huwal-Haiyul-Qayyumu, wa atubu ilaihi
أسْتَغْفِرُ اللهَ الَّذِي لا إلَهَ إلا هُوَ الحَيُّ القَيُومُ وَأتُوبُ إلَيهِ
I seek the forgiveness of Allah, there is no true god except Allah, the Ever-Living, the Self-Subsisting, and I turn to Him in repentance
his sins will be forgiven even if he should have run away from the battlefield (while he was engaged in fighting for the Cause of Allah).”
[Abu Dawud, At-Tirmidhi and Al-Hakim (on conditions of Al-Bukhari and Muslim for accepting Hadith)].
Authentic Dua & Dhikr 