Sahih Muslim 535
Sahih Muslim · Book 5: The Book of Mosques and Places of Prayer · The recommendation to place the hands on the knees when bowing, and the abrogation of tatbiq
Mus'ab b. Sa'd b. Abu Waqqas reported:
حَدَّثَنِي الْحَكَمُ بْنُ مُوسَى ، حَدَّثَنَا عِيسَى بْنُ يُونُسَ ، حَدَّثَنَا إِسْمَاعِيلُ بْنُ أَبِي خَالِدٍ، عَنِ الزُّبَيْرِ بْنِ عَدِيٍّ ، عَنِ مُصْعَبِ بْنِ سَعْدِ بْنِ أَبِي وَقَّاصٍ ، قَالَ صَلَّيْتُ إِلَى جَنْبِ أَبِي فَلَمَّا رَكَعْتُ شَبَّكْتُ أَصَابِعِي وَجَعَلْتُهُمَا بَيْنَ رُكْبَتَىَّ فَضَرَبَ يَدَىَّ فَلَمَّا صَلَّى قَالَ قَدْ كُنَّا نَفْعَلُ هَذَا ثُمَّ أُمِرْنَا أَنْ نَرْفَعَ إِلَى الرُّكَبِ .
I said prayer by the side of my father. When I bowed I intertwined my fingers and placed them between my knees. He struck my hands. When he completed the prayer he said: We used to do that but then were commanded to lift (our palms) to the knees.