The mark of earth was seen on the forehead and nose of the Messenger of Allah (ﷺ)

Reference: Sunan Abi Dawud 894

Sunan Abi Dawud 894
Abu sa’ld al-Khudri said:

The mark of earth was seen on the forehead and nose of the Messenger of Allah (ﷺ) due to the prayer in which he led the people.

حَدَّثَنَا ابْنُ الْمُثَنَّى، حَدَّثَنَا صَفْوَانُ بْنُ عِيسَى، حَدَّثَنَا مَعْمَرٌ، عَنْ يَحْيَى بْنِ أَبِي كَثِيرٍ، عَنْ أَبِي سَلَمَةَ، عَنْ أَبِي سَعِيدٍ الْخُدْرِيِّ، أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم رُئِيَ عَلَى جَبْهَتِهِ وَعَلَى أَرْنَبَتِهِ أَثَرُ طِينٍ مِنْ صَلاَةٍ صَلاَّهَا بِالنَّاسِ ‏.‏
Reference  : Sunan Abi Dawud 894
In-book reference  : Book 2, Hadith 504

Note: These hadith only identify marks of earth on the forehead and nose. Noteably, they do not state that marks were found on the hands, knees or toes.

 
The earth has been made for me a place of prostration and a means of purification

Reference: Sunan an-Nasa'i 736

Sunan an-Nasa'i 736
Jabir bin 'Abdullah said:

"The Messenger of Allah (ﷺ) said: 'The earth has been made for me a place of prostration and a means of purification, so wherever a man of my Ummah is when the time for prayer comes, let him pray.'"

أَخْبَرَنَا الْحَسَنُ بْنُ إِسْمَاعِيلَ بْنِ سُلَيْمَانَ، قَالَ حَدَّثَنَا هُشَيْمٌ، قَالَ حَدَّثَنَا سَيَّارٌ، عَنْ يَزِيدَ الْفَقِيرِ، عَنْ جَابِرِ بْنِ عَبْدِ اللَّهِ، قَالَ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم ‏ "‏ جُعِلَتْ لِيَ الأَرْضُ مَسْجِدًا وَطَهُورًا أَيْنَمَا أَدْرَكَ رَجُلٌ مِنْ أُمَّتِي الصَّلاَةَ صَلَّى ‏"‏ ‏.‏
Reference  : Sunan an-Nasa'i 736
In-book reference  : Book 8, Hadith 49

Note: Carpets were available in the time of the Prophet (ﷺ). These Hadith suggest he refrained from using them.

 
The companions prostrated on stones for convenience.

Reference: Sunan Abi Dawud 399

Sunan Abi Dawud 399
Narrated Jabir ibn Abdullah:

I would offer my noon prayer with the Messenger of Allah (ﷺ) and took a handful of gravels so that they might become cold in my hand and I placed them (before me) so that I may put my forehead on them at the time when I would prostrate. I did this due to the intensity of heat.

حَدَّثَنَا أَحْمَدُ بْنُ حَنْبَلٍ، وَمُسَدَّدٌ، قَالاَ حَدَّثَنَا عَبَّادُ بْنُ عَبَّادٍ، حَدَّثَنَا مُحَمَّدُ بْنُ عَمْرٍو، عَنْ سَعِيدِ بْنِ الْحَارِثِ الأَنْصَارِيِّ، عَنْ جَابِرِ بْنِ عَبْدِ اللَّهِ، قَالَ كُنْتُ أُصَلِّي الظُّهْرَ مَعَ رَسُولِ اللَّهِ صلى الله عليه وسلم فَآخُذُ قَبْضَةً مِنَ الْحَصَى لِتَبْرُدَ فِي كَفِّي أَضَعُهَا لِجَبْهَتِي أَسْجُدُ عَلَيْهَا لِشِدَّةِ الْحَرِّ ‏.
Reference  : Sunan Abi Dawud 399
In-book reference  : Book 2, Hadith 9
 
The companions prostrated on clothing only in exceptional circumstances. Putting the face on the earth was the norm and the expectation.

Reference: Sahih al-Bukhari 1208

Sahih al-Bukhari 1208
Narrated Anas bin Malik:

We used to pray with the Prophet (ﷺ) in scorching heat, and if someone of us could not put his face on the earth (because of the heat) then he would spread his clothes and prostrate over them.

حَدَّثَنَا مُسَدَّدٌ، حَدَّثَنَا بِشْرٌ، حَدَّثَنَا غَالِبٌ، عَنْ بَكْرِ بْنِ عَبْدِ اللَّهِ، عَنْ أَنَسِ بْنِ مَالِكٍ ـ رضى الله عنه ـ قَالَ كُنَّا نُصَلِّي مَعَ النَّبِيِّ صلى الله عليه وسلم فِي شِدَّةِ الْحَرِّ، فَإِذَا لَمْ يَسْتَطِعْ أَحَدُنَا أَنْ يُمَكِّنَ وَجْهَهُ مِنَ الأَرْضِ بَسَطَ ثَوْبَهُ فَسَجَدَ عَلَيْهِ‏.‏
Reference  : Sahih al-Bukhari 1208
In-book reference  : Book 21, Hadith 12
 
Quran: "The followers of the Messenger, on their faces they bear the marks of their prostrations."
Quran: Surah Al-Fath (48:29)
Translation: Abdul Haleem

Muhammad is the Messenger of God. Those who follow him are harsh towards the disbelievers and compassionate towards each other. You see them kneeling and prostrating, seeking God’s bounty and His good pleasure: on their faces they bear the marks of their prostrations. This is how they are pictured in the Torah and the Gospel: like a seed that puts forth its shoot, becomes strong, grows thick, and rises on its stem to the delight of its sowers. So God infuriates the disbelievers through them; God promises forgiveness and a great reward to those who believe and do righteous deeds.

مُّحَمَّدٌۭ رَّسُولُ ٱللَّهِ ۚ وَٱلَّذِينَ مَعَهُۥٓ أَشِدَّآءُ عَلَى ٱلْكُفَّارِ رُحَمَآءُ بَيْنَهُمْ ۖ تَرَىٰهُمْ رُكَّعًۭا سُجَّدًۭا يَبْتَغُونَ فَضْلًۭا مِّنَ ٱللَّهِ وَرِضْوَنًۭا ۖ سِيمَاهُمْ فِى وُجُوهِهِم مِّنْ أَثَرِ ٱلسُّجُودِ ۚ ذَلِكَ مَثَلُهُمْ فِى ٱلتَّوْرَىٰةِ ۚ وَمَثَلُهُمْ فِى ٱلْإِنجِيلِ كَزَرْعٍ أَخْرَجَ شَطْـَٔهُۥ فَـَٔازَرَهُۥ فَٱسْتَغْلَظَ فَٱسْتَوَىٰ عَلَىٰ سُوقِهِۦ يُعْجِبُ ٱلزُّرَّاعَ لِيَغِيظَ بِهِمُ ٱلْكُفَّارَ ۗ وَعَدَ ٱللَّهُ ٱلَّذِينَ ءَامَنُوا۟ وَعَمِلُوا۟ ٱلصَّلِحَتِ مِنْهُم مَّغْفِرَةًۭ وَأَجْرًا عَظِيمًۢا ‎
 
The hadith of the seven bones only explains how to perform sujood, it does not provide a license to prostrate on carpet.

Reference: Sahih al-Bukhari 812

Sahih al-Bukhari 812
Narrated Ibn `Abbas:

The Prophet (ﷺ) said, "I have been ordered to prostrate on seven bones i.e. on the forehead along with the tip of the nose and the Prophet (ﷺ) pointed towards his nose, both hands, both knees and the toes of both feet and not to gather the clothes or the hair."

حَدَّثَنَا مُعَلَّى بْنُ أَسَدٍ، قَالَ حَدَّثَنَا وُهَيْبٌ، عَنْ عَبْدِ اللَّهِ بْنِ طَاوُسٍ، عَنْ أَبِيهِ، عَنِ ابْنِ عَبَّاسٍ، رضى الله عنهما قَالَ قَالَ النَّبِيُّ صلى الله عليه وسلم ‏ "‏ أُمِرْتُ أَنْ أَسْجُدَ عَلَى سَبْعَةِ أَعْظُمٍ عَلَى الْجَبْهَةِ ـ وَأَشَارَ بِيَدِهِ عَلَى أَنْفِهِ ـ وَالْيَدَيْنِ، وَالرُّكْبَتَيْنِ وَأَطْرَافِ الْقَدَمَيْنِ، وَلاَ نَكْفِتَ الثِّيَابَ وَالشَّعَرَ ‏"‏‏.‏
Reference  : Sahih al-Bukhari 812
In-book reference  : Book 10, Hadith 207