Sunan Abi Dawud, Book 3, Hadith 746 (USC-MSA) ⓘ

Narrated Abdullah ibn Mas'ud: The Messenger of Allah taught us how to pray. He then uttered the takbir (Allah is most great) and raised his hands; when he bowed, he joined his hands and placed them between his knees. When this (report) reached Sa'd, he said: My brother said truly. We used to do this; then we were later on commanded to do this, that is, to place the hands on the knees.

حَدَّثَنَا عُثْمَانُ بْنُ أَبِي شَيْبَةَ، حَدَّثَنَا ابْنُ إِدْرِيسَ، عَنْ عَاصِمِ بْنِ كُلَيْبٍ، عَنْ عَبْدِ الرَّحْمَنِ بْنِ الأَسْوَدِ، عَنْ عَلْقَمَةَ، قَالَ قَالَ عَبْدُ اللَّهِ عَلَّمَنَا رَسُولُ اللَّهِ صلى الله عليه وسلم الصَّلاَةَ فَكَبَّرَ وَرَفَعَ يَدَيْهِ فَلَمَّا رَكَعَ طَبَّقَ يَدَيْهِ بَيْنَ رُكْبَتَيْهِ قَالَ فَبَلَغَ ذَلِكَ سَعْدًا فَقَالَ صَدَقَ أَخِي قَدْ كُنَّا نَفْعَلُ هَذَا ثُمَّ أُمِرْنَا بِهَذَا يَعْنِي الإِمْسَاكَ عَلَى الرُّكْبَتَيْنِ ‏.‏