On the authority of Mu’adh ibn Jabal, peace and blessings of Allah be upon him reported: I was with the Prophet and we woke up one day and I said, “O Messenger of Allah, tell me about a deed that will enter me into Paradise and keep me away from the Fire.” The Prophet, peace and blessings be upon him, said:
لَقَدْ سَأَلْتَنِي عَنْ عَظِيمٍ وَإِنَّهُ لَيَسِيرٌ عَلَى مَنْ يَسَّرَهُ اللَّهُ عَلَيْهِ تَعْبُدُ اللَّهَ وَلَا تُشْرِكْ بِهِ شَيْئًا وَتُقِيمُ الصَّلَاةَ وَتُؤْتِي الزَّكَاةَ وَتَصُومُ رَمَضَانَ وَتَحُجُّ الْبَيْتَ
You have asked about an enormous matter, yet it is easy for one whom Allah makes it easy. Worship Allah and do not associate anything with Him, establish the prayer, give the charity, fast the month of Ramadan, and perform pilgrimage to the House.
The Prophet, peace and blessings of Allah be upon him replied by saying:
أَلَا أَدُلُّكَ عَلَى أَبْوَابِ الْخَيْرِ الصَّوْمُ جُنَّةٌ وَالصَّدَقَةُ تُطْفِئُ الْخَطِيئَةَ كَمَا يُطْفِئُ الْمَاءُ النَّارَ وَصَلَاةُ الرَّجُلِ مِنْ جَوْفِ اللَّيْلِ
Shall I not tell you about the gates of goodness? Fasting which is a shield, charity which extinguishes sins just as water extinguishes fire, and the prayer of a man in the late night.
The Prophet recited the verse:
تَتَجَافَى جُنُوبُهُمْ عَنْ الْمَضَاجِعِ حَتَّى بَلَغَ يَعْمَلُونَ
They arise from their beds and supplicate to their Lord in fear and hope and they spend from what We have provided them, for no soul knows what has been hidden for them of comfort as reward for what they used to do.
Surah As-Sajda 32:16
Then the Prophet said:
أَلَا أُخْبِرُكَ بِرَأْسِ الْأَمْرِ كُلِّهِ وَعَمُودِهِ وَذِرْوَةِ سَنَامِهِ
Shall I not tell you about the head of the matter and its peak?
I said, “Of course, O Messenger of Allah.” The Prophet said:
رَأْسُ الْأَمْرِ الْإِسْلَامُ وَعَمُودُهُ الصَّلَاةُ وَذِرْوَةُ سَنَامِهِ الْجِهَادُ
The head of the matter is Islam, its pillar is the prayer, and struggle (jihad) is its peak.
Then the Prophet said:
أَلَا أُخْبِرُكَ بِمَلَاكِ ذَلِكَ كُلِّهِ
Shall I not tell you how to achieve all of this?
I said, “Yes, O Messenger of Allah.” The Prophet took hold of his tongue and he said:
كُفَّ عَلَيْكَ هَذَا
I said, “O Prophet of Allah, will what we say be held against us?” The Prophet said:
ثَكِلَتْكَ أُمُّكَ يَا مُعَاذُ وَهَلْ يَكُبُّ النَّاسَ فِي النَّارِ عَلَى وُجُوهِهِمْ أَوْ عَلَى مَنَاخِرِهِمْ إِلَّا حَصَائِدُ أَلْسِنَتِهِمْ
May your mother be bereaved of you, O Mu’adh! Is there anything that topples people onto their faces in the Hellfire except the harvest of their tongues?
Source: Sunan At-Tirmidhi 2616