Sahih Bukhari
Sahih Bukhari Volume 001, Book 010, Hadith Number 509.
Hadith Section/Book: Sahih Bukhari Sahih Bukhari Book 10. Times of the Prayers
Narated By Anas : The Prophet said, "Do the prostration properly and do not put your fore-arms flat with elbows touching the ground like a dog. And if you want to spit, do not spit in front, nor to the right for the person in prayer is speaking in private to his Lord."