These are the sayings and movements of the Sunnah of Ab'adh in prayer

In the Shafii school, there are 3 elements in prayer. First, the pillars of prayer. Second, sunnah ab'adh. Third, sunnah haiat.

In the Sunnah ab'adh Fiqh Encyclopedia it is stated,

وأبعاض الصّلاة في اصطلاح الشّافعيّة : هي السّنن الّتي تجبر بسجود السّهو ، وهي القنوت في الصّبح ، أو في وتر نصف رمضان ، والقيام له ، والتّشهّد الأوّل ، وقعوده ، والصّلاة على النّبيّ صلى الله عليه وسلم على الأظهر

Suah ab'adh in prayer is the term syafiiyah. Those are the prayers that can be covered by prostration of sahwi. Among them, qunut at dawn, or when witr in the middle of Ramadan, standing up when qunut, reading early tasyahud, sitting early tasyahud, and reading shalawat to the Prophet sallallaahu 'alaihi wa sallam according to strong opinions. (al-Mausu'ah al-Fiqhiyah, 8/126).

If translated, which includes the sunnah ab'adh are:

1. Sitting tasyahud early

2. Reading the initial tasyahud, starting at-Tahiyatu lillaah… until wa ashhadu anna muhammadan 'abduhu wa Rasuluh,

3. Reading shalawat for the Prophet sallallaahu 'alaihi wa sallam after reading the initial tasyahud. That is reading Allahumma shalli 'ala Muhammad.

4. Reading shalawat for the family of the Prophet sallallaahu 'alaihi wa sallam after reading the final tasyahud. Starting from wa 'ala Aali Muhammad to innaka hamidum majid.

5. Qunut when i'tidal in the second rak'ah of the dawn prayer and when witr after the middle of Ramadan.

6. Stand up when qunut.

(al-Mu'tamad fi al-Fiqh as-Shafii, 1/309)

Then what if this sunnah ab'adh is not fulfilled?

According to Syafiiyah, leaving the sunnah ab'adh is makruh but does not include canceling the prayer. If it is not performed on purpose or by mistake, then it must be replaced with prostration sahwi. Allahu a'lam.