If during obligatory prayers one intentionally recites one of the four surahs that contain an obligatory sajdah – as mentioned in Ruling 354 – it is obligatory that he perform sajdah after reciting the verse of sajdah. However, based on obligatory precaution, by performing the sajdah his prayer becomes invalid, and it is obligatory that he perform the prayer again unless he performed the sajdah forgetfully.
If he does not perform the sajdah, he can continue with the prayer but he will have sinned for not performing the sajdah.