Is the reward for wearing the hijab contingent upon a vow of success?

A Muslim woman's adherence to the hijab is an obligation by the origin of Sharia. However, vowing to perform an already obligatory act is not binding according to the majority of scholars. If she fulfills this obligation, she should thank Allah the Almighty for it and ask Him for more of His blessings. She should intend by this act to comply with His command and avoid His prohibition, and she will be rewarded for it.