Answered by Shaykh Amjad Rasheed
Many students of knowledge have asked whether omitting a sura after the fatiha in the prayer necessitates a prostration of forgetfulness. From the books of our imams, it seems that it isn’t necessary to do so and that it invalidates the prayer, because it is adding an integral to the prayer. However Shaykh Nuh added in his translation of the “Maqasid” of Imam al-Nawawi, that omitting a sura does necessitate the prostration of forgetfulness.
An answer has come to me about this and the upshot is that the decided position of the school is that leaving something of the forms of the prayers such as the dhikrs during the ruku` and the sajda do not necessitate the prostration of forgetfulness, as was said in the Minhaj. Even if one does prostrate for it, one’s prayer would be invalidated unless it was done forgetfully or if one was excused because of being ignorant of it, as is mentioned in the Tuhfa (2/174).
Reciting a sura is from the forms of the prayer as is obvious, so its omission does not require the prostration of forgetfulness. The erudite scholar, Al-Bajuri mentioned this in his super-commentary (1/195) at the saying of Ibn Qasim, “(And as for the form) such as the glorifications and the like, that do not necessitate the prostration of forgetfulness (one does not return) the person who is praying (to it) after having left it (and does not prostrate for forgetfulness for it) whether he left it intentionally or forgetfully.
Imam al-Bajuri also said, (and like it) i.e. the sayings of Allahu Akbar between movements, and the recitation of a sura, and the seeking of refuge, and the opening supplication, etc, are forms .(and one does not prostrate out of forgetfulness for them), if he does prostate for them, intentionally, it invalidates his prayer and if not, then it does not. However, because of this [s. omission] the prayer becomes imperfect that necessitates another prostration of forgetfulness.
I reviewed this specific issue with our abovementioned shaykh {s. Shaykh Nuh Keller}, and he said that the mistake had appeared in the new edition of Maqasid because of those he had reviewed it with.
Amjad Rasheed
[Translated by Shazia Ahmad]