It is a sin from the point of view of personal life. Listen to the following four principles which are the base of this Fourth Aspect.
First Principle: When you know your way and opinions to be true, you have the right to say, “My way is right and the best.” But you do not have the right to say, “Only my way is right.” According to the sense of “The eye of contentment is too dim to perceive faults; It is the eye of anger that exhibits all vice;” your unjust view and distorted opinion cannot be the all-decisive judge and cannot condemn the belief of another as invalid.
Second Principle: It is your right that all that you say should be true, but not that you should say all that is true. For one of insincere intention may sometimes take unkindly to advice, and react against it unfavourably.
Third Principle: If you wish to nourish enmity, then direct it against the enmity in your heart, and attempt to rid yourself of it. Be an enemy to your evil-commanding soul and its caprice and attempt to reform it, for it inflicts more harm on you than all else. Do not engage in enmity against other believers on account of that injurious soul. Again, if you wish to cherish enmity, there are unbelievers and atheists in great abundance; be hostile to them. In the same way that the attribute of love is fit to receive love as its response, so too enmity will receive enmity as its own fitting response. If you wish to defeat your enemy, then respond to his evil with good. For if you respond with evil, enmit y will increase, and even though he will be outwardly defeated, he will nurture hatred in his heart and hostility will persist. But if you respond to him with good, he will repent and become your friend. The meaning of the lines: “If you treat the noble nobly, he will be yours; And if you treat the vile nobly, he will revolt,” is that it is the mark of the believer to be noble, and he will become submitted to you by noble treatment.
And even if someone is apparently ignoble, he is noble with respect to his belief. It often happens that if you tell an evil man, “You are good, you are good,” he will become good; and if you tell a good man, “You are bad, you are bad,” he will become bad. Hearken, therefore, to these sacred principles of the Qur’an, for happiness and safety are to be found in them:
If they pass by futility, they pass by it in honourable disdain.(25:72) * If you forgive, pardon, and relent, verily God is All-Relenting, Merciful.(64:14)
Fourth Principle: Those who cherish rancour and enmity transgress against their own souls, their brother believer, and divine mercy. For such a person condemns his soul to painful torment with his rancour and enmity. He imposes torment on his soul whenever his enemy receives some bounty, and pain from fear of him. If his enmit y arises from envy, then it is the most severe form of torment. For envy in the first place consumes and destroys the envier, and its harm for the one envied is either slight or nonexistent.
 ‘Ali Mawardi, Adab al-Dunya wa’l-Din, 10; Diwan al-Shafi’i, 91.
 Mutanabi. See, al-‘Urf al-Tayyib fi Sharh Diwan al-Tayyib, ii, 710.