Man Lā Yaḥḍuruh al-Faqīh
Hadith 605605 - وَقَالَ زُرَارَةُ بْنُ أَعْيَنَ قَالَ أَبُو جَعْفَرٍ عَلَيْهِ اَلسَّلاَمُ: «كَانَ اَلَّذِي فَرَضَ اَللَّهُ عَزَّ وَ جَلَّ عَلَى اَلْعِبَادِ عَشْرَ رَكَعَاتٍ وَ فِيهِنَّ اَلْقِرَاءَةُ وَ لَيْسَ فِيهِنَّ وَهْمٌ يَعْنِي سَهْوٌ فَزَادَ رَسُولُ اَللَّهِ صَلَّى اَللَّهُ عَلَيْهِ وَ آلِهِ سَبْعاً وَ فِيهِنَّ اَلسَّهْوُ وَ لَيْسَ فِيهِنَّ اَلْقِرَاءَةُ فَمَنْ شَكَّ فِي اَلْأَوَّلَتَيْنِ أَعَادَ حَتَّى يَحْفَظَ وَ يَكُونَ عَلَى يَقِينٍ وَ مَنْ شَكَّ فِي اَلْأَخِيرَتَيْنِ عَمِلَ بِالْوَهْمِ.
Hadith.605 - Zurarah ibn A'yan narrated that Imam Muhammad ibn Ali Al-Baqir (as) said:
"What Allah (swt), the Mighty and Majestic, initially made obligatory upon His servants were ten rak'ahs (units of prayer), in which there is recitation and no room for doubt (meaning no room for forgetfulness or error).
The Messenger of Allah (sw) added seven rak'ahs, in which forgetfulness may occur but there is no obligatory recitation.
So, whoever doubts during the first two (rak'ahs) must repeat (the prayer) until they are certain. However, if one doubts in the last two (rak'ahs), they should act according to their assumption."