Sunan at-Tirmithiy كتاب الصلاة باب ما جاء فى نشرالأصابع عند التكبير

حَدَّثَنَا إِسْحَاقُ بْنُ مَنْصُورٍ أَخْبَرَنَا عَبْدُ الرَّحْمَنِ بْنُ مَهْدِىٍّ حَدَّثَنَا شُعْبَةُ عَنِ الْحَكَمِ عَنْ إِبْرَاهِيمَ عَنْ عَلْقَمَةَ عَنْ عَبْدِ اللَّهِ بْنِ مَسْعُودٍ أَنَّ النَّبِىَّ صلى الله عليه وسلم صَلَّى الظُّهْرَ خَمْسًا فَقِيلَ لَهُ أَزِيدَ فِى الصَّلاَةِ فَسَجَدَ سَجْدَتَيْنِ بَعْدَ مَا سَلَّمَ. قَالَ أَبُو عِيسَى هَذَا حَدِيثٌ حَسَنٌ صَحِيحٌ.
The Prophet, peace and blessings of God be upon him, prayed five units of prayer in the noon prayer[1]. He was asked, "Was the prayer increased?" So he prostrated twice[2] after he had pronounced the salutation.
[1] (Thuhr) second prescribed prayer of the day, which normally consists of four units. [2] Prostrations of forgetfulness: two prostrations performed at the end of the prayer when the person realizes that part of the prayer was inadvertently missed or performed incorrectly.