270 – Imam Aḥmad, Abū Dāwūd, and al-Nasāʾī transmit—by way of ʿAbdullāh ibn Jaʿfar—as a hadith traced back to the Prophet: “Whoever becomes uncertain about his prayer should perform two prostrations after giving the salām.” Ibn Khuzaymah declared it authentic (1).

• Grading of the hadith:
  The report is weak. Al-Ḥāfiẓ Ibn Ḥajar states in Fath al-Bārī that its chain is feeble because it passes through Muṣʿab ibn Shaybah, concerning whom there is criticism. Aḥmad said, “He narrates repudiated reports.” Abū Ḥātim commented, “He is not strong.” Al-Nasāʾī judged him “munkar al-ḥadith,” and al-Dāraqutnī said, “He is neither strong nor reliable.”

Al-Munḏirī, however, noted—regarding those who accepted the hadith in his Tahdhīb Sunan Abī Dāwūd—that Muslim used Muṣʿab as evidence in his Ṣaḥīḥ, and Yaḥyā ibn Saʿīd held him to be trustworthy. For this reason Shaykh Aḥmad Shākir declared the narration sound in his commentary on the Musnad.

• Points derived from the hadith:
  1 – Doubt in prayer—whether by addition or omission—is one of the causes that require the prostrations of forgetfulness.
  2 – Therefore, if a worshipper is unsure whether he has prayed, say, three rakʿahs or two, or if he doubts whether he has performed an essential pillar, he should disregard the doubt, act on what is certain, complete what he is unsure of, and then perform the two prostrations of forgetfulness (sujūd al-sahw) after the salām.
  3 – It has been mentioned that a dominant assumption outweighs mere doubt. When the worshipper has a preponderant opinion, he should act upon it and treat it as certainty; this view is the stronger one. Otherwise, the madhhab holds that a predominance of