Does the imam return to the first tashahhud if he stands up having forgotten it?

Question:
Honorable Shaykh, may Allah grant you success. A questioner says: If the imam stands up for the third rak'ah without sitting for the tashahhud and then stands, is it prescribed that he return if he is reminded?

Answer:
If he did not rely on standing, then it is obligatory for him to return. However, if he relied on standing and began the rak'ah he stood up for, he does not return, but he performs the prostration for forgetfulness. The prostration for forgetfulness rectifies this deficiency. Yes.