It is narrated from Sayyiduna Anas (may Allah be pleased with him) that the Messenger of Allah (peace and blessings of Allah be upon him) said: "There are three types of oppression: (1) One type of oppression which Allah will never leave unpunished, (2) one type of oppression which He will forgive, and (3) one type of oppression which will not be forgiven. (Their details are as follows:) The oppression which will never be left unpunished is shirk (associating partners with Allah), which Allah will not forgive. The oppression which will be forgiven is the oppression committed between Allah and His servant. And the oppression which will not be forgiven is the oppression that people commit against each other. Allah will certainly ensure that some (of the oppressed) take retribution from others (the oppressors)."