Man Lā Yaḥḍuruh al-Faqīh
Hadith 850851 - وَ رَأَى ص نُخَامَةً فِي اَلْمَسْجِدِ فَمَشَى إِلَيْهَا بِعُرْجُونٍ مِنْ عَرَاجِينِ اِبْنِ طَابٍ فَحَكَّهَا ثُمَّ رَجَعَ اَلْقَهْقَرَى فَبَنَى عَلَى صَلاَتِهِ وَقَالَ اَلصَّادِقُ عَلَيْهِ اَلسَّلاَمُ «وَ هَذَا يَفْتَحُ مِنَ اَلصَّلاَةِ أَبْوَاباً كَثِيرَةً.
Hadith.851 - The Prophet (sw) saw phlegm (or a spittle) in the mosque. He walked over to it with a palm branch from the branches of Ibn Tab and scraped it off, then returned backward and continued his prayer.
And Imam Jafar ibn Muhammad Al-Sadiq (as) said: "This opens many doors regarding (permissible) actions during prayer."