What is the ruling on ceasing to perform acts of worship—such as fasting and giving charity—for fear of falling into ostentation (riya'), given the desire for people to see the doer of good as righteous? And what is the ruling on internal hatred and cursing of someone, if it is not followed by harm in word or deed?

One must beware of the whispers of Satan that call for abandoning good deeds out of fear of showing off. Working for people is polytheism, and abandoning it is showing off. One must strive against their self to increase good deeds and seek sincerity. There is no sin in disliking a specific person without causing them harm. Love and hate should be based on religion and obedience to Allah.