The ruling on one who forgets and greets a person who enters upon him during the prayer

The questioner : Based on this rule, what do you say, my brother? A man was praying, and a friend of his entered and greeted him. The one praying said, "Peace be upon you," forgetting that he was in prayer. We say: Did you hear them? His prayer is invalid. He was forgetting.

The Shaykh : Did we not say a moment ago that if the prohibited things are done while a person is ignorant or forgetting, there is no sin in them and no effect?

The questioner : Perhaps he is excepted from speaking in the row.

The Shaykh : Perhaps he is from the two sides?

The questioner : I mean, Allah knows best, he forgot the speech from the beginning.

The Shaykh : All right, my uncle, bring us evidence.

The questioner : That, Allah knows best, speaking in the prayer is prohibited.

The Shaykh : It is known that this prayer is not valid with any of the speech of the people.

The questioner : Yes.

The Shaykh : Correct, but if speaking is a prohibited thing that is forbidden, and the rule with us is that if the forbidden thing is done while the person is excused by ignorance or forgetfulness, then it has no effect. The person is not blamed and nothing results from it. Do you understand this rule, everyone? Apply this rule to the issue you asked me about. His friend greeted him, and he said, "Peace be upon you, and Allah's mercy and blessings," forgetting.

The questioner : But, Shaykh, wait for the speech.

The Shaykh : O Merciful, we benefit from them.

The questioner : The fire, what?

The Shaykh : It is , were it not for this hadith, speaking would have been lawful, because the Companions, at first, one of them would speak to his companion next to him in the prayer. I give you the rule, may Allah reward you with good. The rule is: every thing that is prohibited in worship, if a person does it while forgetting, ignorant, or forced, then there is nothing on him. Take this rule, it resolves everything. So if that is the case, if a person speaks in the prayer while forgetting, his prayer, everyone, is valid. Did you understand?
And the evidence for that is that when Mu'awiyah ibn Hukam entered the prayer, a man from the congregation sneezed and said, "Praise be to Allah." Mu'awiyah said, "May Allah have mercy on you." The people threw their glances at him, meaning they disapproved of him. He said, "I think my mother is one of you, what is your business looking at me? What is your business with me, why are you looking at me?" And he gave them the evil eye. This was my speech. They began to strike their thighs to make them silent, so they were silent. When he finished the prayer, the Prophet (peace and blessings be upon him) called him Did you understand? And he did not order him to repeat it because he was ignorant, and the people are like the ignorant.