Explanation of Riyad al-Salihin-82b

The reciter: Upon our Prophet Muhammad and upon his family and all his Companions.
The author (may Allah have mercy on him) transmitted in the context of the hadiths in the chapter on the prohibition of insulting a Muslim without right " from Abu Dharr (may Allah be pleased with him) that he heard the Messenger of Allah (peace and blessings be upon him) say

When any Muslim accuses another Muslim of sin or of disbelief, the reproach rebounds upon the one who utters it, if the other person is not deserving of it.

لا يرمي رجل رجلا بالفسق أو الكفر إلا ارتدت عليه إن لم يكن صاحبه كذلك

Riyad as-Salihin 1560

Narrated by al-Bukhari, and from Abu Hurayrah (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said

The two who exchange insults, whatever they say is upon the one who started it, until the wronged one transgresses.

المتسابان ما قالا فعل البادي منهما حتى يعتدي المظلوم

Narrated by Muslim "

The Shaykh : In the name of Allah, the Most Gracious, the Most Merciful.
Al-Nawawi (may Allah have mercy on him) said in his book Riyad al-Salihin, in the chapter on the prohibition of insulting a Muslim without right " from Abu Dharr (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) said

If one calls his brother a disbeliever or an open sinner, it rebounds upon him, if his companion is not such.

من دعا أخاه بالكفر أو الفسق عاد عليه ما لم يكن صاحبه كذلك

" This means if you say to a person, "You are an open sinner" or "O open sinner," you become the open sinner, unless he is such. And likewise, if one declares someone a disbeliever and says, "You are a disbeliever" or "O disbeliever," and he is not such, the one who said it becomes the disbeliever.
And in this is evidence that this is among the major sins, because the Prophet (peace and blessings be upon him) threatened this speaker that he would be the one described with this attribute. And on this basis, it is not permissible for a person to say to his believing brother, "O open sinner," or to say, "So-and-so is an open sinner," unless he is such and he intends to warn against him, in which case there is no harm. And likewise, he should not say to him, "O disbeliever," or say, "So-and-so is a disbeliever," for it is not permissible for him to do that unless he is such.
And in it is a warning against declaring Muslims disbelievers without scriptural evidence, contrary to what some people dare to do, and refuge is sought in Allah, who declares someone a disbeliever for the slightest thing, saying, "This is disbelief" and "This is open sinfulness," and the like of that.
And as for the second hadith in today's lesson, it is from Abu Hurayrah that the Prophet (peace and blessings be upon him and his family) said The two who exchange insults is the subject, and "what" is a second subject, and "the action of the one who started" is the predicate of the second subject, and the sentence is the predicate of the first subject. And the meaning is that if the two who exchange insults exchange bad words and abuse, then the sin is upon the one who started it for whatever they said If he transgresses, the sin becomes upon him.
And in this is evidence that it is permissible for a person to insult his companion with what he insulted him with, and not to transgress. And for this reason, when the Prophet (peace and blessings be upon him) said This indicates that if a person is a cause of evil, he will be affected by his evil If he transgresses, it is upon him, and if he takes his right without excess, there is nothing upon him. And success is from Allah.