If a Portion of the Tashahhud is Omitted

Q: Salaah-512: Will sajdah sahw be waajib (compulsory) if a portion of The Tashahhud omitted during either the first or the final Qa'dah?

Answer: Because reciting all of the Tashahhud is Waajib (compulsory), omitting some or most of it will necessitate Sajdah Sahw. And Allaah knows best what is most correct.

Fatawa Rahimiyyah vol.2