Is prostration of forgetfulness obligatory (Wajib) upon someone who intentionally omits a Sunnah act of the prayer?
Chapter on the Two Prostrations of Forgetfulness
Al-Mughni
Book of Prayer
Primary text
Omission of a Sunnah act in prayer, even if done intentionally, does not invalidate the prayer. For the omission of the Sunnah act of recitation volume (loud/silent), the dominant view is that prostration of forgetfulness is not obligatory. This is supported by the fact that this omission is considered the abandonment of a non-obligatory act (Sunnah), and therefore, the subsequent rectification (Sujud) is not obligatory, similar to other Sunan.
Supporting text
The opposing view suggests that prostration is prescribed because it is an omission of a verbal Sunnah, equating it to omitting the Qunut or the first Tashahhud. However, even in this view, the position held by Ahmad is that the prostration becomes recommended (mustahabb) and not obligatory (wajib), as it is a compensation for something that was not obligatory.