fiqhsalatsunnasunna-muakkada
A strongly recommended sunna (muakkada) is a practice the Prophet kept constantly. Forgetting one calls for the prostration of correction; leaving it on purpose is blameworthy but the prayer stays valid. The eight cited by Ibn Ashir: the surah after the Fatiha, loud and silent recitation, the transition takbirat, the tasmi, the first sitting, and the two tashahhuds.