What are the conditions that must be met in a Muslim's deeds for them to be accepted by Allah and for him to be rewarded for them?

The acceptance of acts of worship and the reward for them are contingent upon two conditions: First, sincerity to Allah Almighty, meaning that the intention behind words and deeds is seeking His Countenance, based on His saying: (And they were not commanded except to worship Allah, [being] sincere to Him in religion, inclining to truth), and the Hadith: "Indeed, actions are by intentions." Second, the conformity of the action to the Sharia by following the Prophet, peace and blessings be upon him, based on his saying: "Whoever performs an action which we have not commanded, it is to be rejected." Thus, every action that is not intended for the sake of Allah or does not conform to His law is rejected.