This day, I have perfected your religionforyou and completed My favor upon you, and have chosen for you Islam as your religion…" (Holy Qur'an, 5:3)
The Prophet(Saw) said: "I am leaving you two things and you will never go astray as long as you cling to them -- they are the Book of Allah and my Sunnah." [Reported by Al- Haakim - Sahih].