Muhammad ibn Al-Hasan said: “The interpretation of this narration is that if he remembers that he said: " Bismillah," then his prayer is complete, and he should complete the two testimonies in the manner of fulfillment and does not repeat the prayer. And if he does not remember anything from the tashahhud, he must repeat the prayer if he left it intentionally. And there is nothing in the narration indicating whether he left it forgetfully or intentionally. But if he left it forgetfully and then remembered, it would be obligatory upon him to fulfill the tashahhud as we have explained.”
Commentary #31