Allah commanded His Prophet to tell the people:

[إِنِّى أَنَا النَّذِيرُ الْمُبِينُ]

(I am indeed a plain warner) coming to warn the people of a severe punishment that they will suffer if they reject him, as happened to those nations before them who disbelieved in their Messengers, upon whom Allah sent His punishment and vengeance. In the two Sahihs it is reported from Abu Musa that the Prophet said:

«إِنَّمَا مَثَلِي وَمَثَلُ مَا بَعَثَنِي اللهُ بِهِ كَمَثَلِ رَجُلٍ أَتَى قَوْمَهَ فَقَالَ: يَا قَوْمِ إِنِّي رَأَيْتُ الْجَيْشَ بِعَيْنَيَّ، وَإِنِّي أَنَا النَّذِيرُ الْعُرْيَانُ فَالنَّجَاءَ النَّجَاءَ، فَأَطَاعَهُ طَائِفَةٌ مِنْ قَوْمِهِ فَأَدْلَجُوا وَانْطَلَقُوا عَلَى مُهْلِهِمْ فَنَجَوْا، وَكَذَّبَهُ طَائِفَةٌ مِنْهُمْ فَأَصْبَحُوا مَكَانَهُمْ، فَصَبَّحَهُمُ الْجَيْشُ فَأَهْلَكَهُمْ وَاجْتَاحَهُمْ، فَذَلِكَ مَثَلُ مَنْ أَطَاعَنِي وَاتَّبَعَ مَا جِئْتُ بِهِ وَمَثَلُ مَنْ عَصَانِي وَكَذَّبَ مَا جِئْتُ بِهِ مِنَ الْحَق»

(The parable of myself and that with which Allah has sent me is that of a man who came to his people and said, `O people! I have seen the [invading] army with my own eyes, and I am a naked warner, so escape, escape!' Some of his people obeyed him and set out at nightfall, setting off at a slow pace and managing to escape. Others did not believe him and stayed where they were until the next morning when the [invading] army overtook them and destroyed them, wiping them out. This is the parable of the one who obeys me and follows what I have brought, and the example of the one who disobeys me and rejects the truth that I have brought.)