Is a person sinful for an action when their intention was sound, but its results were unlawful, such as giving an animal to someone and then they mistreat it?

If you give an animal to someone else and entrust them with its care, but they mistreat it, there is no sin upon you, unless you know that they mistreat animals and you predominantly believe that they will not fulfill your trust. In this case, sin would accrue to you. If it is possible to reclaim the animal and save it from harm, you are obligated to do so. The rule is that whoever has a good intention and acts upon a permissible matter does not sin, even if a forbidden matter results from it, unless they know or predominantly believe that the forbidden matter will occur from the other person. It is not permissible to commit a forbidden act, nor to do that which one predominantly believes will result in a forbidden act, even if it is committed by another.