Sunnah.com reference : Book 2, Hadith 147English translation : Book 2, Hadith 267Arabic reference : Book 2, Hadith 269
Narrated Abu Humaid As-Sa'idi (RA):
"I saw Allah's Messenger (ﷺ) when he uttered the Takbir, he placed his hands parallel to his shoulders; and when he bowed down, he rested his hands on his knees, then bent his back. When he raised his head up, he stood erect until the bones of his spine became straight. When he prostrated, he placed his arms such that they were neither spread out nor drawn in, and the tips of his toes were facing the Qiblah; when he sat up, at the end of two Rak'a, he sat on his left foot and put erect the right one; and when he sat up after the last Rak'a he put forward the left foot, put erect the other one and sat on his buttock."

[Reported by al-Bukhari].
وَعَنْ أَبِي حُمَيْدٍ اَلسَّاعِدِيِّ ‏- رضى الله عنه ‏- قَالَ : { رَأَيْتُ اَلنَّبِيَّ ‏- صلى الله عليه وسلم ‏-إِذَا كَبَّرَ جَعَلَ يَدَيْهِ حَذْوَ مَنْكِبَيْهِ , وَإِذَا رَكَعَ أَمْكَنَ يَدَيْهِ مِنْ رُكْبَتَيْهِ , ثُمَّ هَصَرَ ظَهْرِهِ , فَإِذَا رَفَعَ رَأْسَهُ اِسْتَوَى حَتَّى يَعُودَ كُلُّ فَقَارٍ مَكَانَهُ , فَإِذَا سَجَدَ وَضَعَ يَدَيْهِ غَيْرَ مُفْتَرِشٍ وَلَا قَابِضِهِمَا , وَاسْتَقْبَلَ بِأَطْرَافِ أَصَابِعِ رِجْلَيْهِ اَلْقِبْلَةَ , وَإِذَا جَلَسَ فِي اَلرَّكْعَتَيْنِ جَلَسَ عَلَى رِجْلِهِ اَلْيُسْرَى وَنَصَبَ اَلْيُمْنَى , وَإِذَا جَلَسَ فِي اَلرَّكْعَةِ اَلْأَخِيرَةِ قَدَّمَ رِجْلَهُ اَلْيُسْرَى وَنَصَبَ اَلْأُخْرَى , وَقَعَدَ عَلَى مَقْعَدَتِهِ }  أَخْرَجَهُ اَلْبُخَارِيُّ  1‏‏1 ‏- صحيح .‏ رواه البخاري (828)‏ .‏ و"هصر " : أي : ثناه في استواء من غير تقويس .‏ قاله الخطابي.‏