حَدَّثَنَا عَلِيُّ بْنُ مُحَمَّدٍ، حَدَّثَنَا وَكِيعٌ، عَنْ مِسْعَرٍ، عَنْ مَنْصُورٍ، عَنْ إِبْرَاهِيمَ، عَنْ عَلْقَمَةَ، عَنْ عَبْدِ اللَّهِ، قَالَ قَالَ رَسُولُ اللَّهِ ـ صلى الله عليه وسلم ـ ‏"‏ إِذَا شَكَّ أَحَدُكُمْ فِي الصَّلاَةِ فَلْيَتَحَرَّ الصَّوَابَ ثُمَّ يَسْجُدْ سَجْدَتَيْنِ ‏"‏ ‏.‏ قَالَ الطَّنَافِسِيُّ هَذَا الأَصْلُ وَلاَ يَقْدِرُ أَحَدٌ يَرُدُّهُ ‏.‏

It wasnarrated that ‘Abdullah said: “The Messenger of Allah (PBUH)said:‘If anyone of you is uncertain about his prayer, let him try todowhat is correct then let him prostrate twice.’” Tanafisi said: "This is the basic rule, and no one is able to reject it." Translation Not Available

Book Ref: Sunan Ibn Majah Book 5 Hadith 1212
Web Ref:  Sunan Ibn Majah Vol 1 Book 5 Hadith 1212