What are the mandatory components of prayer that require prostration of forgetfulness (Sujud as-Sahw) if omitted forgetfully, and what is the ruling if omitted intentionally?
Chapter on what invalidates the prayer if omitted intentionally or forgetfully
Al-Mughni
Book of Prayer
Primary text
The second category of mandatory components comprises eight acts: glorification in bowing or prostration, saying 'Sami'a Allahu liman hamidah,' saying 'Rabbana wa lakal hamd,' saying 'Rabbighfirli' (for seeking forgiveness), the first tashahhud, and sending blessings upon the Prophet in the final tashahhud. If any of these are omitted intentionally, the prayer is invalidated. If omitted forgetfully, the prostration of forgetfulness is required, based on the hadith of Ibn Bahlah, where the Prophet, peace be upon him, omitted the first tashahhud, did not return to it, but performed two prostrations of forgetfulness while sitting before the final taslim. This indicates these acts are obligatory but rectifiable by prostration upon forgetfulness.
Supporting text
There are two narrations regarding the obligation of these acts: one affirming they are obligatory, supported by Ishaq, and another, held by the majority of jurists, stating they are not obligatory. Al-Shafi'i made an exception, obligating the blessings upon the Prophet and joining it with the pillars. A separate narration from Imam Ahmad aligns with the view that they are obligatory.