Prayer (Kitab Al-Salat)
Dawud :: Book 2 : Hadith 717
Narrated Al-Fadl ibn Abbas:
The Apostle of Allah (peace_be_upon_him) came to us accompanied by Abbas when we were in open country belonging to us. He prayed in a desert with no sutrah in front of him, and a she-ass and a bitch of ours were playing in front of him, but he paid no attention to that.