What do we believe about non-Muslims who did not receive the message of Islam?

Question
I have full faith in my religion Islam, Alhamdulillah. But I have one
question which I constantly ponder over. I want to know the criteria
for which innocent non-Muslims will go to Jannah. Suppose some
non-Muslims are very innocent, poor and deprived of worldly pleasure
whilst they always do good deeds.
Will they still be kept in Jahanam forever? On the other hand Muslims
who do many bad deeds but have little faith will be allowed to enter
into Jannah one day? Do you think this is justified?
Answer
In the Name of Allah, the Most Gracious, the Most Merciful.
As-salāmu 'alaykum wa-rahmatullāhi wa-barakātuh.
Allah Ta'ālā says in the Quran,
{إِنَّ الدِّينَ عِنْدَ اللَّهِ الْإِسْلَامُ }
"Verily the true religion with Allah is Islam"
Quran 3:19
The criterion for everlasting success inthe sight of Allah Ta'ālā is
to bring faithin Islam. One who hasbrought faith in the Oneness of
Allah Ta'ālā and His Messenger SallallaahuAlayhi Wasallam has secured
his life in thehereafter. Nabi Sallallaahu Alayhi Wasallam said,
ثِنْتَانِ مُوجِبَتَانِ قَالَ رَجُلٌ: يَا رَسُولَ اللَّهِ مَا
الْمُوجِبَتَانِ؟ قَالَ: (مَنْ مَاتَ يُشْرِكُ بِاللَّهِ شَيْئًا دَخَلَ
النَّارَ وَمَنْ مَاتَ لَايُشْرِكُ بِاللَّهِ شَيْئادخل الْجنَّة)
"Two things dictate. A person asked, "Oh messenger of Allah, what are
the two dictating things? He said, "Whosoever passed away ascribing
partners to Allah will enter the fire of hell. And whosoever did not
ascribe any partners to Allah will enter paradise."
(Mishkaatul Masaabihvol.1 pg.17; Maktabatul Islami)
Islam is the measure of our eternal success. However determining who
hasIslam is something best known to Allah Ta'ālā. There are some
people who may not expose their Islam due to the circumstances they
face in this world. Considering this fact, it is not correct for
anyone to judge who will be in Jannah or Jahannam. It is quite
possible that those who we think are non-Muslims believe in Allah and
His Messenger SallallaahuAlayhi Wasallam . It isbest to dismiss this
affair as something which is best known to Allah Ta'ālā.
And Allah Ta'āla Knows Best