Sunan an-Nasai Book 12, Hadith 1036

أَخْبَرَنَا هَنَّادُ بْنُ السَّرِيِّ، فِي حَدِيثِهِ عَنْ أَبِي الأَحْوَصِ، عَنْ عَطَاءِ بْنِ السَّائِبِ، عَنْ سَالِمٍ، قَالَ أَتَيْنَا أَبَا مَسْعُودٍ فَقُلْنَا لَهُ حَدِّثْنَا عَنْ صَلاَةِ، رَسُولِ اللَّهِ صلى الله عليه وسلم ‏.‏ فَقَامَ بَيْنَ أَيْدِينَا وَكَبَّرَ فَلَمَّا رَكَعَ وَضَعَ رَاحَتَيْهِ عَلَى رُكْبَتَيْهِ وَجَعَلَ أَصَابِعَهُ أَسْفَلَ مِنْ ذَلِكَ وَجَافَى بِمِرْفَقَيْهِ حَتَّى اسْتَوَى كُلُّ شَىْءٍ مِنْهُ ثُمَّ قَالَ سَمِعَ اللَّهُ لِمَنْ حَمِدَهُ فَقَامَ حَتَّى اسْتَوَى كُلُّ شَىْءٍ مِنْهُ ‏.‏

It was narrated that Salim said:"We came to Abu Mas'ud and said to him: 'Tell us about the prayer of the Messenger of Allah (ﷺ).' He stood in front of us and said the takbir, then when he bowed he placed his palms on his knees and put his fingers lower than that, and he held his elbows out from his sides until every part of him had settled. Then he said: Sami' Allahu liman hamidah, Rabbana wa lakal-hamd (Allah hears those who praise Him, our Lord, and to You be the praise), then he stood up until every part of him had settled