The Messenger of Allah ﷺ said, "Whoever says, 'I seek the forgiveness of Allah the Mighty, there is no god but He, the Ever-Living, the Sustainer, and I turn to Him in repentance,' three times, his sins will be forgiven, even if he had fled from the battlefield."
قال رسول الله ﷺ: من قال: أستغفر الله العظيم الذي لا إله إلا هو الحي القيوم وأتوب إليه ثلاثا غفرت له ذنوبه وإن كان فارا من الزحف.
Ibn Khuzayma related it in Tawakkul (as in Ithaf Mahra 10/438), and Hakim (1/511, and 2/117-118) - and from him Bayhaqi in Dawaat (161) - through various routes from Israil, from Abu Sinan, from Abu Ahwas, from Ibn Masud, who narrated it. Its chain of transmission is sahih. Abu Sinan is Darrar bin Mura Kufi, and Abu Ahwas is Awf bin Malik bin Nadla Jushami. Hakim said in the second location, "This is a sahih hadith according to the criterion of Muslim."A note of caution, the editor of Ithaf Mahra corrected "Abu Sinan" to "Abu Shayban," while noting that both original manuscripts read "from Abu Sinan." This correction is mistaken.Similar in meaning is what was narrated from Bilal bin Yasar bin Zayd, freedman of the Prophet ﷺ, who reported from his father, from his grandfather, that he heard the Prophet ﷺ say, "Whoever says, 'I seek forgiveness from Allah, besides whom there is no god, the Living, the Sustainer, and I turn to Him in repentance,' will be forgiven even if he fled from the battlefield." Abu Dawud (1517) and Tirmidhi (3577) both narrated it from the hadith of Musa bin Ismail, who said, Hafs bin Umar bin Mura Shanni told me, my father Umar bin Mura told me, from Bilal bin Yasar bin Zayd, freedman of the Prophet ﷺ, who said, "I heard my father narrate it to me from my grandfather, that he heard the Prophet ﷺ say," and he related the hadith.Tirmidhi said, "This is a gharib hadith, we do not know it except through this route." And it is as he said, for I have not found anyone who deemed Bilal bin Yasar bin Zayd Qurashi trustworthy, and no one narrated from him except Umar bin Mura Shanni. Ibn Hibban mentioned him among his trustworthy narrators, following his usual practice, and this is why Hafiz said "acceptable," meaning when corroborated. Likewise, his father is unknown, and I have not found any corroborating narration for either of them.In some copies of Abu Dawud, "Bilal" was corrupted to "Hilal." And in the phrase "even if he fled from the battlefield" there is something objectionable, because fleeing from the battlefield is among the major sins.Mention has already been made of many supplications within the comprehensive collections of supplications.