What is the ruling on the prayer of one who omits two takbirs then returns to them, thinking they are a pillar, and performs the prostration of forgetfulness?

"Adding an extra sitting or prostration to the prayer intentionally invalidates it by consensus, because that disrupts the order of the prayer and changes its form. However, if this is done out of ignorance of the ruling, the prayer is not invalidated, and a prostration of forgetfulness (sujud as-sahw) is performed."