Arabic (Original)
أَخْبَرَنَا أَبُو الْحَسَنِ بْنُ بِشْرَانَ بِبَغْدَادَ ثنا إِسْمَاعِيلُ بْنُ مُحَمَّدٍ الصَّفَّارُ ثنا يَحْيَى بْنُ طَالِبٍ أنا مُعَلَّى يَعْنِي ابْنَ مَنْصُورٍ قَالَ فَأَخْبَرَنِي خَالِدٌ عَنْ يُونُسَ عَنِ الْحَسَنِ أَنَّهُ كَانَ لَا يَرَى بِسُؤْرِ الْحِمَارِ وَالْبَغْلِ بَأْسًا
English Translation
The Prophet (peace be upon him) saw phlegm on the wall of the mosque facing the qiblah and scraped it off. He said: "When a servant prays, he is in private conversation with his Lord, so let none of you spit toward the qiblah. Let him spit to his left or under his foot."