Sahih Bukhari
Sahih Bukhari Volume 001, Book 012, Hadith Number 785.
Hadith Section/Book: Sahih Bukhari Sahih Bukhari Book 12. Charecteristics Of Prayer
Narated By Anas bin Malik : The Prophet said, "Be straight in the prostrations and none of you should put his forearms on the ground (in the prostration) like a dog."