Sahih Muslim
The Book Pertaining to the Remembrance of Allah, Supplication, Repentance and Seeking Forgiveness (Kitab Al-Dhikr)
Book Number: 035 / Hadith Number: 6573
'Ali reported that Allah's Messenger (may peace be upon him) said to him: Say," O Allah, direct me to the right path and make me adhere to the straight path," and when you make a mention of right guidance, keep in mind the right path and when you consider of the straight (path), keep in mind the straightness of the arrow.