Sahih Muslim
The Book Pertaining to the Remembrance of Allah, Supplication, Repentance and Seeking Forgiveness (Kitab Al-Dhikr)
Book Number: 035 / Hadith Number: 6515
Abu Malik Ashaja'i reported on the authority of his father that whenever a person embraced Islam, Allah's Messenger (may peace be upon him) instructed him to recilte:" O Allah, grant me pardon, have mercy upon me, direct me to the path of righteousness and provide me sustenance."