In the statement of Al-Fadheel ibn 'Iyaadh in relation to the meaning of Allah's statement: [That He might test you, which of you are best in action.] Qur'an 67;2, he said:

"The most sincere and the most correct." It was said to him: "O, father of Ali, what is the meaning of the most sincere (of actions) and the most correct?" He said: "Verily, any action, though it may be correct, which is not done with sincerity, is not accepted; if it is done with sincerity, but is not correct, it is also not accepted, until it is done both with sincerity, and is correct. The sincere action is the one done purely for the sake of Allah, and the correct action is the one which is in accordance with the sunnah."

It has also been narrated by Ibn Shaaheen from Sa'eed ibn Jubair that he said: "No statement is accepted without action. And no statement and action is accepted without (pure) intention. And no statement and action and intention is accepted unless it is in accordance with the sunnah. This statement has also been narrated from Al-Hassan Al-Basry who used the word "is not valid" instead of "is not accepted".

http://www.java-man.com/pages/books/alhisba.html#THE MEANING OF SUBMITTING ONE'S FACE TO ALLAH