It was narrated that Mus’ab bin Sa’d said:“I bowed (in prayer) beside my father, and I put my hands between my knees. He struck my hand and said: ‘We used to do that, then we were commanded to put them on the knees.’”
حَدَّثَنَا مُحَمَّدُ بْنُ عَبْدِ اللَّهِ بْنِ نُمَيْرٍ، حَدَّثَنَا مُحَمَّدُ بْنُ بِشْرٍ، حَدَّثَنَا إِسْمَاعِيلُ بْنُ أَبِي خَالِدٍ، عَنِ الزُّبَيْرِ بْنِ عَدِيٍّ، عَنْ مُصْعَبِ بْنِ سَعْدٍ، قَالَ رَكَعْتُ إِلَى جَنْبِ أَبِي فَطَبَّقْتُ فَضَرَبَ يَدِي وَقَالَ قَدْ كُنَّا نَفْعَلُ هَذَا، ثُمَّ أُمِرْنَا أَنْ نَرْفَعَ إِلَى الرُّكَبِ .
IbnMaja
Establishing the Prayer and the Sunnah Regarding Them • Hadith 873