How can I exit a prayer if I understand that I have made a mistake?

For instance, if I do not sit after the 3^rd rak’ah and stand up for the 4^th rak’ah while performing the evening prayer, should I end the prayer or can I correct it with sajdah as-sahw? Similarly, what should I do if I stand up for the 5^th rak’ah instead of sitting at the end of the 4^th rak’ah?

Dear Brother / Sister,

The mistakes made in prayer are generally divided into two:

1. If something that invalidates the prayer is done, the prayer is invalidated; it becomes necessary to perform that prayer again. If it is necessary to abandon the prayer due to something, one exits the prayer by saluting to the right and left; then, he performs it again.  

2. If the mistake is not something that invalidates prayer, it is compensated; the prayer is completed by sajdah as-sahw. What you ask is related to the second part.

It is fard to sit in the last rak’ah of every prayer. Therefore, it is necessary to sit in the last rak’ah of two, three, four-prayer rak’ahs. However, what should a person who forgets to sit in the last rak’ah and stands up do?

If a person forgets to sit in the last rak’ah and stands up, he sits down if he remembers it before the prostration of that rak’ah whether he is standing or bowing down. He performs sajdah as-sahw after reading at-Tahiyyat. Then, he reads at-Tahiyyat, salawat and other supplications; after that, he ends his prayer.

If a person forgets to sit in the last rak’ah and stands up, he has to perform that prayer again if he remembers it after the prostrations of that rak’ah.

Questions on Islam