What should someone do if they are unsure how many rak‘ahs they prayed?
Short answer
If neither number seems more likely, the person should build on what is certain, which is the lower number, complete the prayer, and perform sujud al-sahw.
Evidence and explanation
The cited answer instructs the worshipper to build on certainty when unsure about the number of rak‘ahs and then perform the prostrations of forgetfulness.
Scholar referenced
This editorial summary is based on the original source linked below and is not presented as a verbatim quotation from the scholar.
From the text of the answer (Arabic, with an English translation)
Original answer — Shaykh ‘Abd al-‘Aziz ibn Baz
حكم من شك في عدد الركعات التي صلاها — فتوى ١٨٢٣٧- Question
«تقول: وأنا أصلي نسيت كم صليت في الركعتين الأولى من الصلاة، هل أقرأ التشهد، وأصلي سجود السهو، ثم أكمل الصلاة، أو لا أكمل، وبعدها أصلي سجود السهو؟ جزاكم الله خيرًا.»
English translation (unreviewed): She says: While I was praying I forgot how many I had prayed in the first two rak'ahs. Do I recite the tashahhud and perform the prostration of forgetfulness and then complete the prayer, or do I not complete it, and perform the prostration of forgetfulness afterwards? May Allah reward you.
- From the text of the answer
«إذا شك المصلي سواء كان رجلًا أو امرأة إذا شك هل هو في الثانية أو في الأولى من المغرب، أو الظهر، أو العصر، أو العشاء، أو الفجر؛ يجعلها الأولى، يبني على اليقين إذا شك المصلي رجلًا كان أو امرأة في الركعة التي هو فيها، هل هي الأولى أو الثانية؟»
English translation (unreviewed): If the worshipper, man or woman, doubts whether he is in the second or the first rak'ah of Maghrib, Zuhr, 'Asr, 'Isha' or Fajr, he counts it as the first, building on certainty. If the worshipper, man or woman, doubts about the rak'ah he is in, whether it is the first or the second?
The Arabic excerpts matched the original page word for word by an automated check and have not had human scholarly review. The English translations are unreviewed translations made for this site; they are not an approved Shari‘ah translation. Rely on the Arabic original.
Source
Ruling when a person doubts the number of rak‘ahs prayed
Shaykh ‘Abd al-‘Aziz ibn Baz, may Allah have mercy on him