Spitting in the mosque is a sin and it is expiated by burying the spittle.  

أَنَّ النَّبِيَّ ﷺ قَالَ التَّفْلُ فِي الْمَسْجِدِ خَطِيئَةٌ وَكَفَّارَتُهُ أَنْ تُوَارِيَهُ  

The Messenger of Allah ﷺ said: Spitting in the mosque is a sin and it is expiated by burying the spittle.  

قَالَ رَسُولُ اللَّهِ ﷺ الْبُزَاقُ فِي الْمَسْجِدِ خَطِيئَةٌ وَكَفَّارَتُهَا دَفْنُهَا  

The Messenger of Allah ﷺ said: Spitting phlegm in the mosque... The narrator then transmitted the rest of the tradition to the same effect.  

قَالَ رَسُولُ اللَّهِ ﷺ النُّخَاعَةُ فِي الْمَسْجِدِ فَذَكَرَ مِثْلَهُ  

The Messenger of Allah ﷺ said: if anyone enters the mosque, and spits in it, or ejects phlegm, he should remove some earth and bury it there. If he does not do so, then he should spit in his clothes and not come out with it.  

قَالَ رَسُولُ اللَّهِ ﷺ مَنْ دَخَلَ هَذَا الْمَسْجِدَ فَبَزَقَ فِيهِ أَوْ تَنَخَّمَ فَلْيَحْفِرْ فَلْيَدْفِنْهُ فَإِنْ لَمْ يَفْعَلْ فَلْيَبْزُقْ فِي ثَوْبِهِ ثُمَّ لْيَخْرُجْ بِهِ  

The Messenger of Allah ﷺ said: When a man stands with the intention of saying prayer, or if any of you says prayer, he should not spit before him, nor at his right side; but he should do so at his left side, if there is a place for it; or he should spit under his left foot and then rub it off.  

قَالَ رَسُولُ اللَّهِ ﷺ إِذَا قَامَ الرَّجُلُ إِلَى الصَّلاَةِ أَوْ إِذَا صَلَّى أَحَدُكُمْ فَلاَ يَبْزُقْ أَمَامَهُ وَلاَ عَنْ يَمِينِهِ وَلَكِنْ عَنْ تِلْقَاءِ يَسَارِهِ إِنْ كَانَ فَارِغًا أَوْ تَحْتَ قَدَمِهِ الْيُسْرَى ثُمَّ لْيَقُلْ بِهِ  

One day while the Messenger of Allah ﷺwas giving sermon he suddenly saw phlegm on the wall towards the qiblah(the direction to which Muslims turn in prayer) of the mosque. So he became angry at people. He then scraped it and sent for saffron and stained with it. He then said: When any one of you prays, Allah, the Exalted, faces him: he, therefore, should not spit before him.  

بَيْنَمَا رَسُولُ اللَّهِ ﷺ يَخْطُبُ يَوْمًا إِذْ رَأَى نُخَامَةً فِي قِبْلَةِ الْمَسْجِدِ فَتَغَيَّظَ عَلَى النَّاسِ ثُمَّ حَكَّهَا قَالَ وَأَحْسِبُهُ قَالَ فَدَعَا بِزَعْفَرَانٍ فَلَطَّخَهُ بِهِ وَقَالَ إِنَّ اللَّهَ قِبَلَ وَجْهِ أَحَدِكُمْ إِذَا صَلَّى فَلاَ يَبْزُقْ بَيْنَ يَدَيْهِ  

The Prophet ﷺ liked the twigs of the date-palm, and he often had one of them in his hand. He entered the mosque and saw phlegm in the wall towards qiblah and he scraped it. He then turned towards people in anger and said: Is any one of you is pleased to spit in his face? When any of you faces qiblah, he indeed faces his Lord, the Majestic the Glorious: the angels are at right side. Therefore, he should not spit on his right side or before him towards qiblah. He should spit towards his left side or beneath his foot. If he is in a hurry, he should do so-and-so. Describing it Ibn ‘Ajlan said: He should spit in his cloth and fold a part of it over the other.  

أَنَّ النَّبِيَّ ﷺ كَانَ يُحِبُّ الْعَرَاجِينَ وَلاَ يَزَالُ فِي يَدِهِ مِنْهَا فَدَخَلَ الْمَسْجِدَ فَرَأَى نُخَامَةً فِي قِبْلَةِ الْمَسْجِدِ فَحَكَّهَا ثُمَّ أَقْبَلَ عَلَى النَّاسِ مُغْضَبًا فَقَالَ أَيَسُرُّ أَحَدَكُمْ أَنْ يُبْصَقَ فِي وَجْهِهِ إِنَّ أَحَدَكُمْ إِذَا اسْتَقْبَلَ الْقِبْلَةَ فَإِنَّمَا يَسْتَقْبِلُ رَبَّهُ جَلَّ وَعَزَّ وَالْمَلَكُ عَنْ يَمِينِهِ فَلاَ يَتْفُلْ عَنْ يَمِينِهِ وَلاَ فِي قِبْلَتِهِ وَلْيَبْصُقْ عَنْ يَسَارِهِ أَوْ تَحْتَ قَدَمِهِ فَإِنْ عَجِلَ بِهِ أَمْرٌ فَلْيَقُلْ هَكَذَا وَوَصَفَ لَنَا ابْنُ عَجْلاَنَ ذَلِكَ أَنْ يَتْفُلَ فِي ثَوْبِهِ ثُمَّ يَرُدَّ بَعْضَهُ عَلَى بَعْضٍ  

A man led the people in prayer. He spat towards qiblah while the Messenger of Allah ﷺ was looking at him. The Messenger of Allah said to the people when he finished his prayer: He should not lead you in prayer (henceforth). Thenceforth he intended to lead them in prayer, but they forbade him and informed him of the prohibition of the Messenger of Allah ﷺ. He mentioned it to the Messenger of Allah ﷺ who said to him: Yes. The narrator said: I think he (the Prophet) said: You did harm to Allah and His Apostle.  

أَحْمَدُ مِنْ أَصْحَابِ النَّبِيِّ ﷺ أَنَّ رَجُلاً أَمَّ قَوْمًا فَبَصَقَ فِي الْقِبْلَةِ وَرَسُولُ اللَّهِ ﷺ يَنْظُرُ فَقَالَ رَسُولُ اللَّهِ ﷺ حِينَ فَرَغَ لاَ يُصَلِّي لَكُمْ فَأَرَادَ بَعْدَ ذَلِكَ أَنْ يُصَلِّيَ لَهُمْ فَمَنَعُوهُ وَأَخْبَرُوهُ بِقَوْلِ رَسُولِ اللَّهِ ﷺ فَذَكَرَ ذَلِكَ لِرَسُولِ اللَّهِ ﷺ فَقَالَ نَعَمْ وَحَسِبْتُ أَنَّهُ قَالَ إِنَّكَ آذَيْتَ اللَّهَ وَرَسُولَهُ  

I came to the Messenger of Allah ﷺ who was saying prayer. He spat beneath his left foot.  

أَتَيْتُ رَسُولَ اللَّهِ ﷺ وَهُوَ يُصَلِّي فَبَزَقَ تَحْتَ قَدَمِهِ الْيُسْرَى  

“He then rubbed it with his shoe."  

عَنْ أَبِيهِ بِمَعْنَاهُ زَادَ ثُمَّ دَلَكَهُ بِنَعْلِهِ  

AbuSa'id said: I saw Wathilah ibn al-Asqa' in the mosque of Damascus. He spat at the mat and then rubbed it with his foot. He was asked: Why did you do so? He said: Because I saw the Messenger of Allah ﷺ doing so.  

لأَنِّي رَأَيْتُ رَسُولَ اللَّهِ ﷺ يَفْعَلُهُ  

We came to Jabir ibn Abdullah who was sitting in his mosque. He said: The Messenger of Allah ﷺ came to us in this mosque and he had a twig of date-palm of the kind of Ibn Tab. He looked and saw phlegm on the wall towards qiblah. He turned to it and scraped it with the twig. He then said: Who of you likes that Allah turns His face from him? He further said: When any of you stands for praying, Allah faces him. So he should not spit before him, nor on his right side. He should spit on his left side under his left foot. If he is in a hurry (i.e. forced to spit immediately), he should do with his cloth in this manner. He then placed the cloth on his mouth and rubbed it off. He then said: Bring perfume. A young man of the tribe stood and hurried to his house and returned with perfume in his palm. The Messenger of Allah ﷺ took it and put it at the end of the twig. He then stained the mark of phlegm with it. Jabir said: This is the reason you use perfume in your mosques.  

أَتَانَا رَسُولُ اللَّهِ ﷺ فِي مَسْجِدِنَا هَذَا وَفِي يَدِهِ عُرْجُونُ ابْنِ طَابٍ فَنَظَرَ فَرَأَى فِي قِبْلَةِ الْمَسْجِدِ نُخَامَةً فَأَقْبَلَ عَلَيْهَا فَحَتَّهَا بِالْعُرْجُونِ ثُمَّ قَالَ أَيُّكُمْ يُحِبُّ أَنْ يُعْرِضَ اللَّهُ عَنْهُ بِوَجْهِهِ ثُمَّ قَالَ إِنَّ أَحَدَكُمْ إِذَا قَامَ يُصَلِّي فَإِنَّ اللَّهَ قِبَلَ وَجْهِهِ فَلاَ يَبْصُقَنَّ قِبَلَ وَجْهِهِ وَلاَ عَنْ يَمِينِهِ وَلْيَبْزُقْ عَنْ يَسَارِهِ تَحْتَ رِجْلِهِ الْيُسْرَى فَإِنْ عَجِلَتْ بِهِ بَادِرَةٌ فَلْيَقُلْ بِثَوْبِهِ هَكَذَا وَوَضَعَهُ عَلَى فِيهِ ثُمَّ دَلَكَهُ ثُمَّ قَالَ أَرُونِي عَبِيرًا فَقَامَ فَتًى مِنَ الْحَىِّ يَشْتَدُّ إِلَى أَهْلِهِ فَجَاءَ بِخَلُوقٍ فِي رَاحَتِهِ فَأَخَذَهُ رَسُولُ اللَّهِ ﷺ فَجَعَلَهُ عَلَى رَأْسِ الْعُرْجُونِ ثُمَّ لَطَخَ بِهِ عَلَى أَثَرِ النُّخَامَةِ قَالَ جَابِرٌ فَمِنْ هُنَاكَ جَعَلْتُمُ الْخَلُوقَ فِي مَسَاجِدِكُمْ