Sahih Bukhari
Sahih Bukhari Volume 004, Book 053, Hadith Number 334.
Hadith Section/Book: Sahih Bukhari Sahih Bukhari Book 53. One-Fifth Of Booty to the Cause Of Allah (Khumus)
Narated By 'Abdullah bin 'Umar : Once I went upstairs in Hafsa's house and saw the Prophet answering the call of nature with his back towards the Qibla and facing Sham.