Imam Ibn Taymiyyah
Worship, obedience, uprightness, necessity of adhering to the Straight Path etc. are from the names by which one and the same is intended and which have two basic principles.
* One of them is that nothing be worshipped except Allah.
* The other is that He be worshipped by what He ordered and legislated, not with innovations.
Allah the Exalted says: “So whoever would hope for the meeting with his Lord – let him do righteous work and not associate in the worship of his Lord anyone.”
“Yes, , whoever submits his face in Islam to Allah while being a doer of good will have his reward with his Lord. And no fear will there be concerning them, nor will they grieve.” And He says: “And who is better in religion than one who submits himself to Allah while being a doer of good and follows the religion of Abraham, inclining toward truth? And Allah took Abraham as an intimate friend.”
Righteous deed is al-ihsaan, which is performance of good actions, and good actions are what Allah and His Messenger love, which, in turn, is what He ordered from obligatory and recommended matters. So whatever is from innovations in religion, i.e. that is not legislated, Allah and His Messenger do not love it, and it cannot be from good actions, and righteous deeds. Just as performing impermissible actions – such as acts of indecency and oppression – is not from good deeds and righteous actions.
As for His saying: “…and (let him) not associate in the worship of his Lord anyone” and His saying, “who submits his face to Allah”, it is being sincere to Him in religion. `Umar ibn al Khattab used to say: “O Allah, make all of my actions righteous, and make them sincere for your Face, and do not make in them anything for anyone .”
Al Fudayl ibn `Iyyad said about His saying: “To test you which of you is best in action.” , “Most sincere and most proper (action)” They said: “O Abu Alee, what action is most sincere and most proper?” He said: “Verily, an action that is done sincerely and is not proper is not accepted, and when it is proper and not done sincerely it is (also) not accepted. Sincere (action) is one that is for Allah, and proper is one that is in accordance with the Sunnah.”