He writes in al-Kulliyyāt: “Neither nabaʾ nor inbāʾ appears in the Qur’an except in connection with something of moment and great consequence.”

– ana bashar (I am a human being): the ordinary states of humanity befall me and the human condition applies to me.

– bashar: pronounced with two short vowels, a word that carries several meanings; what is meant here is simply “a human being,” whether male or female, singular or plural.

– ansā (I forget): linguistically, nisyān (forgetfulness) is the opposite of remembrance and retention. Technically, it is the heart’s heedlessness of a matter—a transient ignorance that removes one’s knowledge of something while he still remembers other things, thus excluding sleep and the like. Nisyān can also mean “to leave or abandon,” as in the verse, “They forgot Allah, so He forgot them” (Qur’an 9:67).

– idhā shakka aḥadukum (if any one of you is uncertain): in language, shakk is the opposite of certainty. Technically, it is the state in which the two possibilities of knowing and not knowing are evenly balanced, so that one does not incline to either side. When one of the two sides becomes stronger and outweighs the other, it is called ẓann (conjecture).

– fal-yataḥarrā aṣ-ṣawāb (let him strive to determine what is correct): taḥarrī is the deliberate effort and diligence in seeking, coupled with the resolve to single something out in word and deed.

– fal-yutimma ʿalayhi (let him complete [his prayer] on that basis): that is, let him finish while building upon it. Were the verb itmam (completion) not imbued with the sense of “building upon,” it would not be permissible to use it with the preposition ʿalā.

Lessons derived from the hadith
1 – The hadith relates that the Prophet ﷺ once performed one of the four-rakʿah prayers as five. The Companions did not alert him, thinking that a divine modification adding a rakʿah might have occurred. When he ended with the salām they asked, “Has something new occurred in the prayer?” He replied, “And what is that?” They said, “You prayed five,” whereupon he folded his legs beneath him, faced the qiblah, performed two prostrations, and then gave salām again.

2 – The hadith demonstrates that the two prostrations of forgetfulness are prescribed for an unintentional addition during the prayer and that the prayer need not be repeated; rather, the two prostrations of forgetfulness are offered, thereby compensating for the deficiency in the prayer.