حَدَّثَنَا عَمْرُو بْنُ رَافِعٍ، حَدَّثَنَا إِسْمَاعِيلُ ابْنُ عُلَيَّةَ، عَنْ هِشَامٍ، حَدَّثَنِي يَحْيَى، حَدَّثَنِي عِيَاضٌ، أَنَّهُ سَأَلَ أَبَا سَعِيدٍ الْخُدْرِيَّ فَقَالَ أَحَدُنَا يُصَلِّي فَلاَ يَدْرِي كَمْ صَلَّى ‏.‏ فَقَالَ قَالَ رَسُولُ اللَّهِ ـ صلى الله عليه وسلم ـ ‏"‏ إِذَا صَلَّى أَحَدُكُمْ فَلَمْ يَدْرِ كَمْ صَلَّى فَلْيَسْجُدْ سَجْدَتَيْنِ وَهُوَ جَالِسٌ ‏"‏ ‏.‏

‘Iyadnarrated that he asked Abu Sa’eed Al-Khudri: “One of us praysandhe does not know how many (Rak’ah) he has prayed.” He said: “TheMessenger of Allah (PBUH) said: ‘When anyone of you prays and doesnotknow how many he has prayed, let him perform two prostrationswhile heis sitting.’” Translation Not Available

Book Ref: Sunan Ibn Majah Book 5 Hadith 1204
Web Ref:  Sunan Ibn Majah Vol 1 Book 5 Hadith 1204