Sahih al-Bukhari · Hadith 790
حدثنا ابو الوليد، قال حدثنا شعبة، عن ابي يعفور، قال سمعت مصعب بن سعد، يقول صليت الى جنب ابي فطبقت بين كفى ثم وضعتهما بين فخذى، فنهاني ابي وقال كنا نفعله فنهينا عنه، وامرنا ان نضع ايدينا على الركب
Narrated Mus`ab bin Sa`d:I offered prayer beside my father and approximated both my hands and placed them in between the knees. My father told me not to do so and said, "We used to do the same but we were forbidden (by the Prophet) to do it and were ordered to place the hands on the knees