Is hating a Muslim, bearing malice towards him, or striking him considered a sin, and does making a Muslim happy with a kind word or a gift earn reward?

Malice is a reprehensible characteristic, and there are hadiths that forbid it and warn against those who harbor it. Among them is what the Prophet, peace and blessings be upon him, mentioned: "There are three (qualities), if a person does not have one of them, then Allah will forgive him whatever else He wills: he who dies without associating anything with Allah, and was not a sorcerer following sorcerers, and did not harbor malice towards his brother."

One who harms people through insults, beating, consuming their wealth, or shedding their blood, commits a sin. The bankrupt person is he who comes on the Day of Resurrection with prayer, fasting, and zakat, but he insulted this one, beat that one, consumed the wealth of this one, and shed the blood of that one. So, this one will take from his good deeds, and that one will take from his good deeds. If his good deeds are exhausted before what he owes is settled, then some of the sins of his companion will be taken and cast upon him, and then he will be cast into the Fire.

Islam encourages all types of good deeds. Every good deed a person does for another is considered an act of charity for him. "For every living creature with a moist liver, there is a reward." Among the actions considered charity are: judging justly between two people, helping a man with his mount, a good word, a step towards prayer, and removing harm from the road.

The condition for the acceptance of a deed and the attainment of reward for it is that it must be purely for Allah. Allah, the Almighty, said: "So whoever hopes for the meeting with his Lord, let him do righteous work and not associate anyone in the worship of his Lord."