Sahih Al Bukhari Hadith Number 790

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.”

10  Call to Prayers (Adhaan)
Hadith number 790
Volume no 1
Chapter: 118 (To put the hands (palms) on both knees while bowing.)