If you forget to stand without the last meeting or sit in the third rak'ah, do sijdah sahu 4623175462

(A) The prayer will be performed as described. However, after reciting Tashahhud or Attahiyatu, one has to perform Sahu in Sijdah with Salam on the right side. Then you have to recite Attahiyatu, Darood Sharif and Masura in Dua and return the salutation. (B) In the prayer of four rak'ats, if the Imam forgets the third rak'at and sits for three tasbeehs, he should give sahu in sijdah. And if he is sitting for less than that time, then he does not have to give sahu in prostration. (C) It is makrooh to intentionally perform sahu in prostration without necessity. However, if it is not known whether Sahu comes in Sijdah due to some mistake or not, Sahu Sijdah can be done as a precaution. And he is safe from the last leg ... and prostrates for the last leg and the rest of the obligations are there, all the duties and obligations in the neighborhood. (الدر المختار: 1/469) 8448864896