Answered by Shaykh Ilyas Patel
If one is in the tashahhud position and one accidentally recites surah fatihah, stopping and then reading the correct tashahhud recitation, completing the prayer, does one need to make any correction of the prayer?
In the Name of Allah, Most Merciful & Compassionate
In the above case when one has read Surah Fatiha instead of the dua of Tashahhud (which is the place when one sits in the sitting position (qa’da) then one will have to do the forgetfulness prostration (sajda sahw) to make up the delay for not reading the dua of Tashhuud on time.
It is mentioned in the commentaries of Quduri as follows:
If one makes a mistake by omitting the following duas: Thana, Ta’awwudh, the takbirat of ruku and sujud and their tasbih, then one will not do the forgetfulness prostration, except one makes a mistake in five things: Takbirat of Eidayn, Qunut, Tashahhud, Recitation and delaying the salam from its place.
(Al-Jawhara and other commentaries of Quduri)
(Al-Mu’tasar al-Daruri Shar al-Quduri, pg 138)