The Book Pertaining to the Remembrance of Allah, Supplication, Repentance and Seeking Forgiveness (Kitab Al-Dhikr)
Muslim :: Book 35 : Hadith 6574
This hadith has been narrated on the authority of 'Asim b. Kulaib with the same chain of transmitters that Allah's Messenger (may peace be upon him) said to me: Say:" O Allah, I beg of Thee righteousness and adhering to the straight path."