Mistreating animals is considered a sin in Islam. A Muslim is responsible for the care of animals so much so that an ill-treated animal will testify against the one who abused it on the Day of Judgment. Islam forbids branding animals and killing them in vain, such as for sport. The Prophet Muhammad forbade people to capture birds, burn anthills, and whip animals. Even in slaughtering animals for food, Islam requires that the slaughtering be done according to Islamic procedure, which is humane and aims to cause the animals as little suffering as possible. As humans, we have a responsibility towards every living creature.
So whosoever does good equal to the weight of an atom, shall see it.