What is injustice, and how do I know that I have wronged someone?

Injustice is the act of putting something in a place it doesn't belong, exceeding the bounds of what is right, and transgressing against others in their wealth and honor. It is divided into three categories: The greatest of these is associating partners with Allah (Shirk), which is the injustice of a servant concerning the rights of Allah. The second is a servant's injustice to himself through sins, both major and minor. The third is a servant's injustice to his brethren by transgressing against their rights, wealth, honor, and lives.