How should an individual praying alone 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 individual praying alone doubts the number of rak'ahs after salaming, the established ruling is to build upon certainty (al-yaqin) and perform the necessary additional rak'ahs, followed by two prostrations of forgetfulness before the final salutation. This is derived from the Hadith of Abu Sa'id al-Khudri and 'Abd al-Rahman ibn 'Awf, which advises discarding doubt and acting upon what is certain. This ensures the prayer is not considered deficient, fulfilling the principle of 'La Gharar fi as-Salah' (There is no harm in prayer).
Supporting text
There is a view attributed to Ahmad that an individual praying alone should also follow their strongest conjecture, similar to the Imam, based on a reconciliation of the various Hadiths. If the two matters (certainty and conjecture) are equal in the case of the Imam, he should also build upon certainty.