Intending to shorten Salah and offering it in full out of forgetfulness
If you are traveling for a distance of eighty kilometers or more, it will be better for you to shorten the four-Rak‘ah Salah (Prayer consisting of four units) to two Rak‘ahs. There is nothing wrong if you offer it as complete.
If you intend to shorten the Salah when saying Takbirat-ul-Ihram (saying: "Allahu Akbar [Allah is the Greatest]" upon starting Prayer) but then forget and rise to offer the third Rak‘ah, you have either the choice to continue offering the Salah as complete four-Rak‘ahs; in this case you are not required to offer Sujud-ul-Sahw, or you may sit, recite the Tashahhud, say the Taslim, and then offer Sujud-ul-Sahw.May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.