The Glorified Allah has stated in Quran that He will not forgive the sin of shirk, which means joining others with Allah, attributing some of His features to them and showing them a kind of respect that should only be shown to Him. Allah commands:
“Surely, Allah does not forgive joining others with Him, but He forgives what is less than that for whom He wills. And he, who joins others with Allah, has certainly slanders Allah with a tremendous sin.” (An-Nisa / The Women 4:48)
It is clearly seen in this verse that Allah may forgive any sin but shirk, for whom He wills. For the ones He doesn’t will, He will punish them according to their sins.
The violation of a person’s rights is subject to “rightful due” and it is one of the big sins. Allah has stated that He can forgive all of the sins of a person except shirk. So this rule also includes forgiving of the rightful due. In the meantime Allah will also recompense and persuade the aggrieved party. But If Allah does not forgive the sins of someone and he/she also has the sin of rightful due, what will be their position? Our Prophet explains it like as follows:
“Whoever violates a rightful due of another person, the violator should ask for aggrieved party’s blessing immediately. Because money will not be valid on the Day of Judgment. Hence the good deeds of the violator will be taken and transferred to the aggrieved party. If the violator does not have any good deeds then the sins of aggrieved party would be taken and transferred to the violator.” (Bukhari, Riqaq/Specifics, 48)
Muslims should not violate the rights of other people. If a sin like that is committed, one should immediately ask for the aggrieved party’s blessing and the forgiveness of Allah. The important thing is to work for being one of the ones that are going to be forgiven from all of their sins by Allah in the hereafter.