Answered by Ustadh Sufyan Qufi
How do you perform it? Do you have to say the tashahhud, do you have to do it before or after the taslim, and if you omit something obligatory from prayer then what?
In the name of Allah, Most Compassionate, Most Merciful.
I pray this finds you in the best of states.
The Forgetfulness Prostration
From a previous answer at Seekersguidance:
For the forgetfulness prostration [which is necessary if a necessary (wajib) action was left forgetfully and for nothing else]:
1. In the final sitting, recite the tashahhud;
2. Give one salam, to the right;
3. Perform two prostrations, with their sunnas;
4. Sit and repeat the final sitting, in full–reciting the tashahhud, sending blessings, and making supplication (dua); and then
5. End with two salams.
Missing an Obligatory Action of the Prayer
Missing an obligatory (fard) action of the prayer renders the prayer invalid and you will have to repeat it.
The obligatory actions of the prayer are the standing position, the recitation of the Quran, the bowing, the prostration, the last sitting for the extent of reciting the tashahhud. [Shurunbulali, Nur al-Idah]
Please see this answer for more details:
Forgetting to Perform an Obligatory Action of the Prayer
And Allah knows best
[Ustadh] Sufyan Qufi
Checked and Approved by Shaykh Faraz Rabbani
Ustadh Sufyan Qufi is an advanced seeker of knowledge, originally from Algeria, who grew up in France. He began searching far and wide for answers to the fundamental questions of life and was disappointed at the answers he found. Then he connected with various traditional teachers and gradually connected with SeekersGuidance. He embarked on his journey of learning through the various teachers at SeekersGuidance, including his mentor Shaykh Faraz Rabbani. He studied numerous texts in Islamic Law, Theology, Hadith, and other areas with Shaykh Faraz Rabbani and other teachers, including Shaykh Abdurrahman al-Sha‘ar, Shaykh Ali Hani, and others. He is an active instructor at SeekersGuidance and answers questions through the SeekersGuidance Answers Service.