كتاب الطهارة
1  
The Book of Purification
(7)
Chapter: The Manners of Answering the Call of Nature
(7)
باب قضاء الحاجة
Bulugh al-Maram 105
Narrated Suraqa bin Malik (rad):
Allah’s Messenger (ﷺ) educated us about lavatory (manners) that we should sit on our left foot and keep erect our right foot. [Reported by Al-Baihaqi through a chain of weak narrators].
وَعَنْ سُرَاقَةَ بْنِ مَالِكٍ ‏- رضى الله عنه ‏- قَالَ: { عَلَّمْنَا رَسُولُ اَللَّهِ ‏- صلى الله عليه وسلم ‏-فِي اَلْخَلَاءِ: " أَنَّ نَقْعُدَ عَلَى اَلْيُسْرَى, وَنَنْصِبَ اَلْيُمْنَى" } رَوَاهُ اَلْبَيْهَقِيُّ بِسَنَدٍ ضَعِيف ٍ 1‏ .‏


‏1 ‏- ضعيف.‏ رواه البيهقي (1/96)‏.‏

Reference : Bulugh al-Maram 105
In-book reference : Book 1, Hadith 124
English translation : Book 1, Hadith 111