Sometimes in prayer I forget the prostration, and I stand up to recite al-Fatihah, or I forget to recite al-Fatihah. What should I do in this case?

Question:
May Allah reward you with good, and may He do you good. Sometimes in prayer I stand up from a unit, then I forget the prostration, and I stand up to recite al-Fatihah and another surah, or I forget to recite al-Fatihah. What should I do in this case?

Answer:
If one forgets a pillar of the prayer from one of the units, such as reciting al-Fatihah, or bowing, or prostrating, he must return and perform it. He performs it and whatever follows it, and his unit is valid. He performs it and whatever follows it, and his unit is valid. However, if he stands up for the second unit, he does not return; rather, he continues in that unit, and it becomes the first unit for him. The unit from which he left the pillar is invalid. He completes his prayer based on this consideration, and he performs the prostration for forgetfulness.