The one who forgot the prostration -the last one - in his prayer and then repeated it after the closing salam without the tashahhud: Does he repeat the prayer?
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Question:
Honorable Shaykh, may Allah grant you success, the questioner who forgot the prostration while traveling says: Do I repeat the prayer, even though I prostrated but did not perform the final tashahhud?
Answer:
Amen. You repeat the prayer because you left a pillar, which is the final tashahhud. If one leaves a pillar, regardless of how close the time is, he performs a complete rak'ah. If it was a long time ago, he repeats the prayer from the beginning. Yes.
Honorable Shaykh, may Allah grant you success, the questioner who forgot the prostration while traveling says: Do I repeat the prayer, even though I prostrated but did not perform the final tashahhud?
Answer:
Amen. You repeat the prayer because you left a pillar, which is the final tashahhud. If one leaves a pillar, regardless of how close the time is, he performs a complete rak'ah. If it was a long time ago, he repeats the prayer from the beginning. Yes.
Source
قناة «العلامة الدكتور صالح الفوزان»، [109 /641] الذي نسي السجدة -الأخيرة - في صلاته ثم أعادها بعد السلام دون تشهد هل يعيد الصلاة؟ — youtube.com
The Arabic text is a machine transcription of the audio recording.