It is narrated from Hazrat Mughirah bin Shu'bah (may Allah be pleased with him) that the Holy Prophet (peace and blessings be upon him) said: When any one of you stands up instead of sitting after two rak'ahs, then if he has not yet stood up straight, he should sit down; but if he has completely stood up, then he should not sit down, and later he should perform sajdah sahw.