Sahih Muslim — The Book Pertaining to the Remembrance of Allah, Supplication, Repentance and Seeking Forgiveness — Hadith No: 6849
Translation
Abu Malik Ashaja'i reported on the authority of his father that whenever a person embraced Islam, Allah's Messenger (ﷺ) instructed him to recilte:" O Allah, grant me pardon, have mercy upon me, direct me to the path of righteousness and provide me sustenance