عَنْ عَبْدِ اللَّهِ بْنِ جَعْفَرٍ رَضِيَ اللَّهُ عَنْهُ عَنِ النَّبِيِّ صَلَّى اللَّهُ عَلَيْهِ وَآلِهِ وَسَلَّمَ قَالَ: ((مَنْ شَكَّ فِي صَلَاتِهِ فَلْيَسْجُدْ سَجْدَتَيْنِ وَهُوَ جَالِسٌ)) وَفِي لَفْظٍ: ((فَلْيَسْجُدْ سَجْدَتَيْنِ بَعْدَ مَا يُسَلِّمُ))
It is narrated from Sayyiduna Abdullah bin Ja'far (may Allah be pleased with him) that the Noble Prophet (peace and blessings be upon him) said: Whoever has doubt in his prayer should perform two prostrations while sitting. In another narration: He should perform two prostrations after saying the salam.