"If one of you is not sure about his prayer, let him estimate what he thinks is most likely to be correct and complete the prayer on that basis, then let him prostrate twice."
The Book of Forgetfulness (In Prayer)
Sunan an-Nasa'i - Hadith Reference: Sunan an-Nasa'i 1240
Hadith Text
"If one of you is not sure about his prayer, let him estimate what he thinks is most likely to be correct and complete the prayer on that basis, then let him prostrate twice."
Commentary (Sharh)
This noble hadith establishes a fundamental principle in Islamic jurisprudence for addressing doubt during prayer. The Prophet (peace be upon him) guides the worshipper to rely upon certainty (yaqeen) when uncertainty (shakk) arises.
The instruction to "estimate what he thinks is most likely to be correct" (fal-yazunn) demonstrates that in matters of worship where doubt occurs, one should act upon the stronger probability. This reflects the Islamic legal maxim that certainty is not overruled by doubt.
The command to "complete the prayer on that basis" emphasizes that once a decision is made through sound estimation, the worshipper should proceed with confidence and not be troubled by lingering doubts, thus preserving the spiritual concentration (khushoo') essential to prayer.
The final injunction to "prostrate twice" refers to the prostrations of forgetfulness (sujood al-sahw), which serve as a corrective measure and expiation for the uncertainty that occurred during the prayer. This comprehensive guidance ensures both the validity of the prayer and the peace of mind of the worshipper.