Abu Dawud
Purification (Kitab Al-Taharah)
Book Number: 001 / Hadith Number: 11
Narated By Abdullah ibn Umar : Marwan al-Asfar said: I saw Ibn Umar make his camel kneel down facing the qiblah, then he sat down urinating in its direction. So I said: AbuAbdurRahman, has this not been forbidden? He replied: Why not, that was forbidden only in open country; but when there is something between you and the qiblah that conceals you , then there is no harm.