Answered by Ustadh Tabraze Azam
Question: Assalam ‘aleykum,
When praying fajr this morning, I couldn’t remember if I performed one or two prostrations. So after tashahud, I got up again and did another cycle of prayer (rakaat) just in case and finished my prayer despite falling into doubts again regarding the number of prostration.
Was my prayer invalidated? And what should I do next time this occurs?
Answer: Wa alaikum assalam wa rahmatullahi wa barakatuh,
I pray that this message finds you well, insha’Allah.
The basis is acting according to your reasonable certainty. There are two answers to the question, “did you prostrate?”: yes or no. There is no other option.
Thus, in your scenario, what was required was for you to make a judgement, and if you had decided that you had only prostrated a single time, you should have prostrated again and then completed your prayer.
In general, when a prostration is missed, it does not negate the entire cycle (rak`at) because doing one prostration after the other is necessary and not obligatory.
[Shurunbulali, Maraqi al-Falah]
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And Allah alone knows best.
Checked & Approved by Shaykh Faraz Rabbani