Abu Malik al-Ashja'i narrates from his father, who said: I heard the Messenger of Allah (peace and blessings be upon him) teaching someone who had accepted Islam; he (peace and blessings be upon him) was saying: "Say: O Allah, forgive me, have mercy on me and provide for me." Then he said: "These words gather the good of this world and the Hereafter."
Hadith Referenceالمعجم الكبير للطبراني / باب الطاء / 8153