How should an Imam reconcile doubt in the number of rak'ahs after salaming?
Chapter on the Two Prostrations of Forgetfulness
Al-Mughni
Book of Prayer
Primary text
If an Imam experiences doubt regarding the number of rak'ahs (whether three or four, for example), the dominant opinion suggests they should act according to their strongest conjecture (ghalib dhann) regarding what was performed, and then perform two prostrations of forgetfulness after the final salutation. This is supported by the narration of Ibn Mas'ud. This is based on the command to strive for the most probable correct action.
Supporting text
A differing narration attributed to Ahmad suggests that the Imam should build upon certainty (al-yaqin) and perform the prostrations before the salutation, similar to a person praying alone. Some scholars, including Kharaqi, differentiate, stating the Imam builds on conjecture while the individual praying alone builds on certainty because the Imam has others to prompt them to the correct course of action.