Leaving the prayer before completing it, under the impression that it has in fact been completed, does not nullify the prayer; one may resume it and make up what is missing.

Speaking during the very body of the prayer out of forgetfulness does not invalidate it, contrary to the scholars who rule otherwise. Dhu al-Yadayn, the Prophet ﷺ, and several worshippers all spoke in such a situation.

What was omitted from the prayer may validly be appended to its beginning, even if a long interval has elapsed. Likewise, if someone forgets a prostration and then does something that normally breaks the prayer—such as talking—it is established in the two Ṣaḥīḥ collections, in the hadith of Ibn Masʿūd traced back to the Prophet ﷺ, that he prostrated after both the salām and the speech.

Movements that are not part of the prayer do not invalidate it, even if they are many, provided they are done out of ignorance or forgetfulness.

The two prostrations of forgetfulness are obligatory for anyone who adds to, or omits from, the prayer; they compensate for the shortcoming and humble Satan.

These prostrations are not repeated, even if several causes meet. The Prophet ﷺ gave the salām having left something out of the prayer, yet still sufficed with only two prostrations.

When the worshipper ends the prayer with a deficiency, the prostrations of forgetfulness are performed after the salām; in all other cases they are done before the salām. This is the Ḥanbalī position, a nuanced ruling that gathers all the evidence, in contrast to those who make every such prostration after the salām (the Ḥanafīs) or every one before the salām (the Shāfiʿīs).

Any lapse on the imam’s part is carried over to the followers, for complete conformity and imitation are required; whatever deficiency befalls the imam’s prayer befalls those praying behind him as well.

Concerning the tashahhud after the two prostrations of forgetfulness, Shaykh al-Islām Ibn Taymiyyah said: “None of the Prophet’s statements include a command to recite the tashahhud after those prostrations, nor do the sound, widely accepted hadiths report that he did so. Had a tashahhud been prescribed, those who narrated the incident would have mentioned it. The sole basis for those who affirm it is the hadith of ʿImrān, which is singular, without a corroborating chain; this undermines its strength.”