Language:
كتاب مواقيت الصلاة
9  
Times of the Prayers
(8)
Chapter: A person in Salat (prayer) is speaking in private to his Lord (Allah)
(8)
باب الْمُصَلِّي يُنَاجِي رَبَّهُ عَزَّ وَجَلَّ
Sahih al-Bukhari 532

Narrated Anas:

The Prophet (ﷺ) said, "Do the prostration properly and do not put your forearms 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."

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 ‏"‏‏.‏
Reference : Sahih al-Bukhari 532
In-book reference : Book 9, Hadith 11
USC-MSA web (English) reference : Vol. 1, Book 10, Hadith 509
  (deprecated numbering scheme)