Al-Kāfi - The Book of Prayer

Chapter: Mistake in Sujud (prostrations) 3ـ عَنْهُ عَنْ أَحْ٠َّدِ بْنِ أَبِي نَصْرٍ وَعَلِيِّ بْنِ ٠َّدٍ عَنْ سَهْلِ بْنِ زِيَادٍ عَنْ أَحْ٠َّدِ بْنِ أَبِي نَصْرٍ عَنْ أَبِي الْحَسَنِ (عَلَيْهِ الْسَّلا٠) قَالَ سَأَلْتُهُ عَنْ رَجُلٍ صَلَّى رَكْعَةً ثُ٠َّ ذَكَرَ وَهُوَ فِي الثَّانِيَةِ وَهُوَ رَاكِعٌ أَنَّهُ تَرَكَ سَجْدَةً ٠ِنَ الأولَى فَقَالَ كَانَ أَبُو الْحَسَنِ (صلّى اللهُ عَلَيْهِ وَآلِه) يَقُولُ إِذَا تَرَكْتَ السَّجْدَةَ فِي الرَّكْعَةِ الأولَى وَلَ٠ْ تَدْرِ وَاحِدَةً أَ٠ْ ثِنْتَيْنِ اسْتَقْبَلْتَ الصَّلاَةَ حَتَّى يَصِحَّ لَكَ أَنَّهُ٠3.

It is a narration from him (narrator of previous Hadith) by Ahmad ibn Muhammad from Ahmad ibn Muhammad ibn abu Nasr and Ali ibn Muhammad from Sahl ibn Ziyad from Ahmad ibn Muhammad ibn abu Nasr who has said the following: “I once asked abu al-Hassan (a.s.), about a man who performs one Rak’at of Salah (prayer), then he remembers in the second Rak’at in Ruku’ (bowing down on one’s knees) position that he has omitted one Sajdah (prostration) of the first Rak’at.

He said, ‘Abu al-Hassan (a.s.), would say that if you omit Sajdah (prostration) in the first Rak’at and do not know if it is one or two; perform Salah (prayer) again until it is correct to say that two Sajdah (prostrations) are performed.’” صحيح - Allamah Baqir al-Majlisi (Mirʾāt al-ʿUqūl fī Sharḥ Akhbār Āl al-Rasūl (5/188))