A man forgot the first tashahhud and performed it in the third rak'ah; is his prayer valid?

Question:
He says: Honorable Shaykh, may Allah grant you success, a man prayed 'Isha' and forgot the first tashahhud, then he performed it in the third rak'ah, and then he completed his prayer. Is his prayer valid? What is its place after the third? The place of the first tashahhud is after the second, so he performed it in a place other than its proper place.

Answer:
He only has to perform sujud al-sahw. If he stood up from the first tashahhud and forgot it, and he relied on standing, then he continues. And if he wants to say the taslim before the actual taslim, he prostrates for forgetfulness, and this suffices for the first tashahhud. As for his sitting for it after the second, this has no value and is not valid in this case. But due to his ignorance, his prayer is valid, and he had to perform sujud al-sahw, but he did not know. His prayer is valid, if Allah wills. Yes.