What does the first heaven comprise of?
What are the sayings of the Qur'an and the Hadith about this?
Also, what are the opinions of the scholars?
If there's any problem in my question please inform me. Thanks!
There are not too many verses in the Qur'an that discuss the nearest sky. The first one is:
إِنَّا زَيَّنَّا السَّمَاءَ الدُّنْيَا بِزِينَةٍ الْكَوَاكِبِ
Indeed, We have adorned the nearest heaven with an adornment of stars
Verse 37:6 says that its adornment is the starts. Scholars of tafsīr say the stars serve as a source of light that adds beauty to the sky, and they are used for navigation.
فَقَضَاهُنَّ سَبْعَ سَمَاوَاتٍ فِي يَوْمَيْنِ وَأَوْحَىٰ فِي كُلِّ سَمَاءٍ أَمْرَهَ وَزَيَّنَّا السَّمَاءَ الدُّنْيَا بِمَصَابِيحَ وَحِفْظًا ذَٰلِكَ تَقْدِيرُ الْعَزِيزِ الْعَلِيمِ
And He completed them as seven heavens within two days and inspired in each heaven its command. And We adorned the nearest heaven with lamps and as protection. That is the determination of the Exalted in Might, the Knowing.
Verse 41:12 says that the seven skies were created in two days and that Allah adorned the nearest one with light sources (the stars).
وَلَقَدْ زَيَّنَّا السَّمَاءَ الدُّنْيَا بِمَصَابِيحَ وَجَعَلْنَاهَا رُجُومًا لِّلشَّيَاطِينِ وَأَعْتَدْنَا لَهُمْ عَذَابَ السَّعِيرِ
And We have certainly beautified the nearest heaven with stars and have made [from] them what is thrown at the devils and have prepared for them the punishment of the Blaze.
Verse 67:5 says essentially the same thing, then it adds that Al-Qurtubi added in his tafsir that angels pelt jinns who try to steal hearings with parts of those stars (see 15:18, 72:8, 37:8, and 37:10).
Likewise, only a few hadith specifically mention the nearest sky:
عن أبي هريرة عن رسول الله صلى الله عليه وسلم قال: يَنْزِلُ اللَّهُ إِلَى السَّمَاءِ الدُّنْيَا كُلَّ لَيْلَةٍ حِينَ يَمْضِي ثُلُثُ اللَّيْلِ الأَوَّلُ فَيَقُولُ أَنَا الْمَلِكُ أَنَا الْمَلِكُ مَنْ ذَا الَّذِي يَدْعُونِي فَأَسْتَجِيبَ لَهُ مَنْ ذَا الَّذِي يَسْأَلُنِي فَأُعْطِيَهُ مَنْ ذَا الَّذِي يَسْتَغْفِرُنِي فَأَغْفِرَ لَهُ فَلاَ يَزَالُ كَذَلِكَ حَتَّى يُضِيءَ الْفَجْرُ
Abu Huraira reported Allah's Messenger (ﷺ) as saying: Allah descends every night to the lowest heaven when one-third of the first part of the night is over and says: I am the Lord; I am the Lord: who is there to supplicate Me so that I answer him? Who is there to beg of Me so that I grant him? Who is there to beg forgiveness from Me so that I forgive him? He continues like this till the day breaks.
Sahih Muslim 6/202 talks about the descent of Allah ﷻ to the lowest heaven to answer the supplications of those who supplicate to him during the last one-third of the night.
كان أبو ذر رضي الله عنه يحدث أن رسول الله صلى الله عليه وسلم قال: فُرِجَ سَقْفِي وَأَنَا بِمَكَّةَ، فَنَزَلَ جِبْرِيلُ ـ عَلَيْهِ السَّلاَمُ ـ فَفَرَجَ صَدْرِي، ثُمَّ غَسَلَهُ بِمَاءِ زَمْزَمَ، ثُمَّ جَاءَ بِطَسْتٍ مِنْ ذَهَبٍ مُمْتَلِئٍ حِكْمَةً وَإِيمَانًا، فَأَفْرَغَهَا فِي صَدْرِي، ثُمَّ أَطْبَقَهُ، ثُمَّ أَخَذَ بِيَدِي فَعَرَجَ إِلَى السَّمَاءِ الدُّنْيَا. قَالَ جِبْرِيلُ لِخَازِنِ السَّمَاءِ الدُّنْيَا افْتَحْ. قَالَ مَنْ هَذَا قَالَ جِبْرِيلُ
Narrated Anas bin Malik that Abu Dhar said: Allah's Messenger (ﷺ) said, "The roof of my house was made open while I was at Makkah (on the night of Mi'raj) and Jibril descended. He opened up my chest and washed it with the water of Zamzam. Then he brought the golden tray full of Wisdom and Belief and poured it in my chest and then closed it. Then he took hold of my hand and ascended to the nearest heaven. Jibril told the gatekeeper of the nearest heaven to open the gate. The gatekeeper asked, "Who is it?" Jibril replied, "I am Jibril."
Sahih al-Bukhari 25/119 talks about the ascent of the Prophet ﷺ on the night of Mi'rāj, and it refers to the nearest sky as a firmament with an access that is guarded.