Mishkat al-Masabih 29
Mu‘adh b. Jabal reported:
I said, “Inform me, messenger of God, of an act which will cause me to enter paradise and remove me far from hell.” He replied, “You have asked a serious question, but it is easy for the one whom God helps to answer it. Worship God, associate nothing with Him, observe the prayer, pay the zakat , fast during Ramadan, and make the Pilgrimage to the House.” He said, “Shall I not guide you to the gateways of what is good? Fasting is a protection, and almsgiving extinguishes sin as water extinguishes fire, and a man's prayer in the middle of the night [has the same effect].” Then he recited, “Withdrawing themselves from their couches ... they have been doing.” 1 Then he said, “Shall I not guide you to the head and support of the matter and the top of its hump?” I replied, “Yes, messenger of God.” He said, “The head of the matter is Islam, its support is prayer, and the top of its hump is jihad .” Then he said, “Shall I not inform you of the controlling of all that?” I replied, “Yes, Prophet of God.” So he took hold of his tongue and said, “Restrain this.” I asked, “Prophet of God, shall we really be punished for what we talk about?” He replied, “I am surprised at you, 2 Mu'adh! Will anything but the harvests of their tongues overthrow men in hell on their faces (or, on their nostrils)?” 

Ahmad, Tirmidhi and Ibn Majah transmitted it. 1 Quran, xxxii, 16f. 2 Literally, may your mother be bereft of you.
عَن معَاذ بن جبل قَالَ كُنْتُ مَعَ النَّبِيِّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ فِي سفر فَأَصْبَحت يَوْمًا قَرِيبا مِنْهُ وَنحن نسير فَقلت يَا رَسُولَ اللَّهِ أَخْبِرْنِي بِعَمَلٍ يُدْخِلُنِي الْجَنَّةَ وَيُبَاعِدنِي عَن النَّار قَالَ لقد سَأَلتنِي عَن عَظِيمٍ وَإِنَّهُ لِيَسِيرٌ عَلَى مَنْ يَسَّرَهُ اللَّهُ عَلَيْهِ تَعْبُدُ اللَّهَ وَلَا تُشْرِكُ بِهِ شَيْئًا وَتُقِيمَ الصَّلَاةَ وَتُؤْتِيَ الزَّكَاةَ وَتَصُومَ رَمَضَانَ وَتَحُجَّ الْبَيْت ثُمَّ قَالَ أَلَا أَدُلُّكَ عَلَى أَبْوَابِ الْخَيْرِ الصَّوْمُ جُنَّةٌ وَالصَّدَقَةُ تُطْفِئُ الْخَطِيئَةُ كَمَا يُطْفِئُ المَاء النَّار وَصَلَاة الرجل من جَوف اللَّيْل قَالَ ثمَّ تَلا (تَتَجَافَى جنُوبهم عَن الْمضَاجِع)
حَتَّى بَلَغَ (يَعْمَلُونَ)
ثُمَّ قَالَ أَلَا أَدُلُّكَ بِرَأْس الْأَمر كُله وَعَمُودِهِ وَذِرْوَةِ سَنَامِهِ قُلْتُ بَلَى يَا رَسُولَ اللَّهِ قَالَ رَأْسُ الْأَمْرِ الْإِسْلَامُ وَعَمُودُهُ الصَّلَاةُ وَذِرْوَةُ سَنَامِهِ الْجِهَادُ ثُمَّ قَالَ أَلَا أُخْبِرُكَ بِمِلَاكِ ذَلِكَ كُلِّهِ قُلْتُ بَلَى يَا نَبِيَّ اللَّهِ فَأَخَذَ بِلِسَانِهِ فَقَالَ كُفَّ عَلَيْكَ هَذَا فَقُلْتُ يَا نَبِيَّ اللَّهِ وَإِنَّا لَمُؤَاخَذُونَ بِمَا نتكلم بِهِ فَقَالَ ثَكِلَتْكَ أُمُّكَ يَا مُعَاذُ وَهَلْ يَكُبُّ النَّاسَ فِي النَّارِ عَلَى وُجُوهِهِمْ أَوْ عَلَى مَنَاخِرِهِمْ إِلَّا حَصَائِدُ أَلْسِنَتِهِمْ. رَوَاهُ أَحْمَدُ وَالتِّرْمِذِيُّ وَابْنُ مَاجَه