"The Messenger of Allah saw some sputum in the prayer direction of the mosque, when he was praying in front of the people. He scratched it off, then when the prayer was over, he said: 'When anyone of you is performing prayer, Allah is before him, so none of you should spit toward the front while praying.'" (Using translation from Ibn Mājah 763)  

رَأَى رَسُولُ اللهِ ﷺ نُخَامَةً فِي قِبْلَةِ الْمَسْجِدِ وَهُوَ يُصَلِّي بَيْنَ يَدَيِ النَّاسِ فَحَتَّهَا ثُمَّ قَالَ حِينَ انْصَرَفَ «إِنَّ أَحَدَكُمْ إِذَا كَانَ فِي الصَّلَاةِ فَإِنَّ اللهَ قِبَلُ وَجْهِهِ فَلَا يَتَنَخَّمَنَّ أَحَدُكُمْ قِبَلَ وَجْهِهِ فِي الصَّلَاةِ»