Allah tells us that out of His justice, He does not punish anyone until He has established proof against him by sending a Messenger to him, as He says:

[تَكَادُ تَمَيَّزُ مِنَ الغَيْظِ كُلَّمَا أُلْقِىَ فِيهَا فَوْجٌ سَأَلَهُمْ خَزَنَتُهَآ أَلَمْ يَأْتِكُمْ نَذِيرٌ - قَالُواْ بَلَى قَدْ جَآءَنَا نَذِيرٌ فَكَذَّبْنَا وَقُلْنَا مَا نَزَّلَ اللَّهُ مِن شَىْءٍ إِنْ أَنتُمْ إِلاَّ فِى ضَلَـلٍ كَبِيرٍ ]

(Every time a group is cast therein, its keeper will ask: "Did no warner come to you'' They will say: "Yes, indeed a warner did come to us, but we belied him and said: `Allah never sent down anything (of revelation); you are only in great error.''') (67:8-9) And,

[وَسِيقَ الَّذِينَ كَـفَرُواْ إِلَى جَهَنَّمَ زُمَراً حَتَّى إِذَا جَآءُوهَا فُتِحَتْ أَبْوَبُهَا وَقَالَ لَهُمْ خَزَنَتُهَآ أَلَمْ يَأْتِكُمْ رُسُلٌ مِّنكُمْ يَتْلُونَ عَلَيْكُمْ ءَايَـتِ رَبِّكُمْ وَيُنذِرُونَكُمْ لِقَـآءَ يَوْمِكُمْ هَـذَا قَالُواْ بَلَى وَلَـكِنْ حَقَّتْ كَلِمَةُ الْعَذَابِ عَلَى الْكَـفِرِينَ ]

(And those who disbelieved will be driven to Hell in groups, till, when they reach it, the gates thereof will be opened. And its keepers will say, "Did not the Messengers come to you from yourselves - reciting to you the verses of your Lord, and warning you of the meeting of this Day of yours'' They will say: "Yes,'' but the Word of torment has been justified against the disbelievers!) (39:71) And,

[وَهُمْ يَصْطَرِخُونَ فِيهَا رَبَّنَآ أَخْرِجْنَا نَعْمَلْ صَـلِحاً غَيْرَ الَّذِى كُـنَّا نَعْمَلُ أَوَلَمْ نُعَمِّرْكُمْ مَّا يَتَذَكَّرُ فِيهِ مَن تَذَكَّرَ وَجَآءَكُمُ النَّذِيرُ فَذُوقُواْ فَمَا لِلظَّـلِمِينَ مِن نَّصِيرٍ ]

(Therein they will cry: "Our Lord! Bring us out, we shall do righteous good deeds, not (the evil deeds) that we used to do.'' (Allah will reply:) "Did We not give you lives long enough, so that whosoever would receive admonition could receive it And the warner came to you. So taste you (the evil of your deeds). For the wrongdoers there is no helper.'') (35:37) There are other Ayat which indicate that Allah will not make anyone enter Hell except after sending a Messenger to them.