Sayyiduna Abdullah bin Mas'ud (may Allah be pleased with him) said: "Whoever says three times: 'I seek the forgiveness of Allah, besides whom there is no true deity, the Ever-Living, the Sustainer of all, and I turn to Him in repentance,' is forgiven, even if he had fled from the battlefield."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 8509