حَدَّثَنَا أَبُو كُرَيْبٍ، حَدَّثَنَا أَبُو خَالِدٍ الأَحْمَرُ، عَنِ ابْنِ عَجْلاَنَ، عَنْ زَيْدِ بْنِ أَسْلَمَ، عَنْ عَطَاءِ بْنِ يَسَارٍ، عَنْ أَبِي سَعِيدٍ الْخُدْرِيِّ، قَالَ قَالَ رَسُولُ اللَّهِ ـ صلى الله عليه وسلم ـ " إِذَا شَكَّ أَحَدُكُمْ فِي صَلاَتِهِ فَلْيُلْغِ الشَّكَّ وَلْيَبْنِ عَلَى الْيَقِينِ فَإِذَا اسْتَيْقَنَ التَّمَامَ سَجَدَ سَجْدَتَيْنِ فَإِنْ كَانَتْ صَلاَتُهُ تَامَّةً كَانَتِ الرَّكْعَةُ نَافِلَةً وَإِنْ كَانَتْ نَاقِصَةً كَانَتِ الرَّكْعَةُ لِتَمَامِ صَلاَتِهِ وَكَانَتِ السَّجْدَتَانِ رَغْمَ أَنْفِ الشَّيْطَانِ " .
It wasnarrated that Abu Sa’eed Al-Khudri said: “The Messenger ofAllah(PBUH) said: ‘If anyone of you is uncertain about his prayer, lethim put aside uncertainty and act upon that which is certain. When hehas made sure his prayer is complete, then let him prostrate twice.Then if his prayer was complete, that (extra) Rak’ah will becountedas voluntary, and if his prayer was lacking, that Rak’ahwill completehis prayer, and the two prostrations will rub theSatan’s nose in thedust.’” Translation Not Available
Book Ref: Sunan Ibn Majah Book 5 Hadith 1210
Web Ref: Sunan Ibn Majah Vol 1 Book 5 Hadith 1210