Sahih Bukhari Volume 1, Book 9, Hadith 532

حَدَّثَنَا حَفْصُ بْنُ عُمَرَ، قَالَ حَدَّثَنَا يَزِيدُ بْنُ إِبْرَاهِيمَ، قَالَ حَدَّثَنَا قَتَادَةُ، عَنْ أَنَسٍ، عَنِ النَّبِيِّ صلى الله عليه وسلم قَالَ ‏"‏ اعْتَدِلُوا فِي السُّجُودِ، وَلاَ يَبْسُطْ ذِرَاعَيْهِ كَالْكَلْبِ، وَإِذَا بَزَقَ فَلاَ يَبْزُقَنَّ بَيْنَ يَدَيْهِ وَلاَ عَنْ يَمِينِهِ، فَإِنَّهُ يُنَاجِي رَبَّهُ ‏"

Narrated 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."