Rajab al-Hanbali (Raheemahullah) mentioned that the great Sufi, Fudayl ibn al-`Iyad (Raheemahullah) explained Allah’s words,
“That He may test which of you is best in action” [Qur’an, 67:2] by saying,
That is, who is sincere in it and correct in it. And the action that is sincere but incorrect is not accepted. And if it is correct and insincere then it is also not accepted. It is only accepted when it is both sincere and correct. And it is only sincere when it is for the sake of Allah Most High, and correct when it is done according to the sunnah.
Read in full Intention: Validity And Sincerity