(118) باب وَضْعِ الأَكُفِّ عَلَى الرُّكَبِ فِي الرُّكُوعِ
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."
Reference: Sahih al-Bukhari 790
In-book reference: Book 10, Hadith 185
USC-MSA web (English) reference(deprecated numbering scheme): Vol. 1, Book 12, Hadith 756