What is the ruling if one stands up from the first prostration without sitting for the separation between the two prostrations, thereby omitting the sitting and the second prostration?
Chapter on the Two Prostrations of Forgetfulness
Al-Mughni
Book of Prayer
Primary text
If one remembers omitting the sitting for separation and the second prostration before beginning the recitation of the next pillar (Qira'ah), one must return. This is the view of Malik and Ash-Shafi'i, and no dissent is known. Upon returning, one must perform the sitting for separation, then the second prostration, and then proceed to the next unit of prayer (Rak'ah). This is because the sitting is obligatory, and standing cannot substitute for it, even if done intentionally.
Supporting text
A minority of Ash-Shafi'i's companions argue that the sitting is not required because the separation has been achieved by standing, but this is incorrect since the sitting is obligatory and standing cannot substitute for it.