How Does A Person Who Forgets First Sitting In Fardh Prayers Complete His Prayer?

How does a person who forgets first sitting in fardh prayers complete his prayer?

First sitting is one of the wajibs of the prayer. One should perform sajdah al-sahw if he forgets to perform a wajib act. It is makruh tahrimi not to perform the first sitting, therefore, such prayer should be re-established (Ibn Nujaym, al-Bahr, I, 310; Ibn Abidin, Radd al-Muhtar, II, 157).

Source: Presidency Of Religious Affairs The Turkey, High Board of Religious Affairs FATWAS