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]‏ .‏