It is permissible to offer voluntary prayers in congregation, and to pray on hasir (palm-fiber mats), khumrah (small mats), cloth, and other pure things

Anas b. Malik reported that his grandmother, Mulaika, invited the Messenger of Allah (ﷺ) to a dinner which she had prepared. He (the Prophet) ate out of that and then said:

Stand up so that I should observe prayer (in order to bless) you Anas b. Malik said: I stood up on a mat (belonging to us) which had turned dark on account of its long use. I sprinkled water over it (in order to soften it), and the Messenger of Allah (ﷺ) stood upon it, and I and an orphan formed a row behind him (the Prophet) and the old woman was behind us, and the Messenger of Allah (ﷺ) led us in two rak'ahs of prayer and then went back.

حَدَّثَنَا يَحْيَى بْنُ يَحْيَى، قَالَ قَرَأْتُ عَلَى مَالِكٍ عَنْ إِسْحَاقَ بْنِ عَبْدِ اللَّهِ بْنِ أَبِي طَلْحَةَ، عَنْ أَنَسِ بْنِ مَالِكٍ، أَنَّ جَدَّتَهُ، مُلَيْكَةَ دَعَتْ رَسُولَ اللَّهِ صلى الله عليه وسلم لِطَعَامٍ صَنَعَتْهُ فَأَكَلَ مِنْهُ ثُمَّ قَالَ ‏

‏ قُومُوا فَأُصَلِّيَ لَكُمْ ‏

‏ ‏.‏ قَالَ أَنَسُ بْنُ مَالِكٍ فَقُمْتُ إِلَى حَصِيرٍ لَنَا قَدِ اسْوَدَّ مِنْ طُولِ مَا لُبِسَ فَنَضَحْتُهُ بِمَاءٍ فَقَامَ عَلَيْهِ رَسُولُ اللَّهِ صلى الله عليه وسلم وَصَفَفْتُ أَنَا وَالْيَتِيمُ وَرَاءَهُ وَالْعَجُوزُ مِنْ وَرَائِنَا فَصَلَّى لَنَا رَسُولُ اللَّهِ صلى الله عليه وسلم رَكْعَتَيْنِ ثُمَّ انْصَرَفَ ‏.‏

Anas b. Malik reported that the Messenger of Allah (ﷺ) wits the best among people in character. On occasions, the time of prayer would come while he was in our house. He would then order to spread the mat lying under him. That was dusted and then water was sprinkled over it. The Messenger of Allah (ﷺ) then led the prayer and we stood behind him, and that mat was made of the leaves of date-palm.

وَحَدَّثَنَا شَيْبَانُ بْنُ فَرُّوخَ، وَأَبُو الرَّبِيعِ، كِلاَهُمَا عَنْ عَبْدِ الْوَارِثِ، قَالَ شَيْبَانُ حَدَّثَنَا عَبْدُ الْوَارِثِ، عَنْ أَبِي التَّيَّاحِ، عَنْ أَنَسِ بْنِ مَالِكٍ، قَالَ كَانَ رَسُولُ اللَّهِ صلى الله عليه وسلم أَحْسَنَ النَّاسِ خُلُقًا فَرُبَّمَا تَحْضُرُ الصَّلاَةُ وَهْوَ فِي بَيْتِنَا فَيَأْمُرُ بِالْبِسَاطِ الَّذِي تَحْتَهُ فَيُكْنَسُ ثُمَّ يُنْضَحُ ثُمَّ يَؤُمُّ رَسُولُ اللَّهِ صلى الله عليه وسلم وَنَقُومُ خَلْفَهُ فَيُصَلِّي بِنَا وَكَانَ بِسَاطُهُمْ مِنْ جَرِيدِ النَّخْلِ ‏.‏

Thabit reported on the authority of Anas:

The Messenger of Allah (ﷺ) came to us and there was none in our house but I, my mother and my aunt Umm Haram. He (the Prophet) said: Stand up so that I may lead you in prayer (and there was no time for prescribed prayer). He led us in prayer. A person said to Thabit: Where stood Anas with him (the Prophet)? He replied: He was on the right side. He then blessed us, the members of the household with every good of this world and of the Hereafter. My mother said: Messenger of Allah (and then, pointing towards Anas, said), here is your little servant, invoke the blessing of Allah upon him too. He then blessed me with every good, and he concluded his blessings for me (with these words): Allah! increase his wealth, and his children and make (them the source of) blessing for him.

حَدَّثَنِي زُهَيْرُ بْنُ حَرْبٍ، حَدَّثَنَا هَاشِمُ بْنُ الْقَاسِمِ، حَدَّثَنَا سُلَيْمَانُ، عَنْ ثَابِتٍ، عَنْ أَنَسٍ، قَالَ دَخَلَ النَّبِيُّ صلى الله عليه وسلم عَلَيْنَا وَمَا هُوَ إِلاَّ أَنَا وَأُمِّي وَأُمُّ حَرَامٍ خَالَتِي فَقَالَ ‏"‏ قُومُوا فَلأُصَلِّيَ بِكُمْ ‏"‏ ‏.‏ فِي غَيْرِ وَقْتِ صَلاَةٍ فَصَلَّى بِنَا ‏.‏ فَقَالَ رَجُلٌ لِثَابِتٍ أَيْنَ جَعَلَ أَنَسًا مِنْهُ قَالَ جَعَلَهُ عَلَى يَمِينِهِ ‏.‏ ثُمَّ دَعَا لَنَا أَهْلَ الْبَيْتِ بِكُلِّ خَيْرٍ مِنْ خَيْرِ الدُّنْيَا وَالآخِرَةِ فَقَالَتْ أُمِّي يَا رَسُولَ اللَّهِ خُوَيْدِمُكَ ادْعُ اللَّهَ لَهُ ‏.‏ قَالَ فَدَعَا لِي بِكُلِّ خَيْرٍ وَكَانَ فِي آخِرِ مَا دَعَا لِي بِهِ أَنْ قَالَ ‏"‏ اللَّهُمَّ أَكْثِرْ مَالَهُ وَوَلَدَهُ وَبَارِكْ لَهُ فِيهِ ‏"‏ ‏.‏

Abdullah b. al-Mukhtar heard Musa b. Anas narrating on the authority of Anas b. Malik that the Messenger of Allah (ﷺ) led him, his mother or his aunt in prayer. He made me, stand on his right side and made the woman stand, behind us.

وَحَدَّثَنَا عُبَيْدُ اللَّهِ بْنُ مُعَاذٍ، حَدَّثَنَا أَبِي، حَدَّثَنَا شُعْبَةُ، عَنْ عَبْدِ اللَّهِ بْنِ الْمُخْتَارِ، سَمِعَ مُوسَى بْنَ أَنَسٍ، يُحَدِّثُ عَنْ أَنَسِ بْنِ مَالِكٍ، أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم صَلَّى بِهِ وَبِأُمِّهِ أَوْ خَالَتِهِ ‏.‏ قَالَ فَأَقَامَنِي عَنْ يَمِينِهِ وَأَقَامَ الْمَرْأَةَ خَلْفَنَا ‏.‏

This hadith has also been narrated by Shu'ba with this chain of transmitters.

وَحَدَّثَنَاهُ مُحَمَّدُ بْنُ الْمُثَنَّى، حَدَّثَنَا مُحَمَّدُ بْنُ جَعْفَرٍ، ح وَحَدَّثَنِيهِ زُهَيْرُ بْنُ حَرْبٍ، قَالَ حَدَّثَنَا عَبْدُ الرَّحْمَنِ، - يَعْنِي ابْنَ مَهْدِيٍّ - قَالَ حَدَّثَنَا شُعْبَةُ، بِهَذَا الإِسْنَادِ ‏.‏

Maimuna, the wife of the Messenger of Allah (ﷺ), reported:

The Messenger of Allah (ﷺ) said prayer while I was by his side, and at times when he prostrated his cloth touched me, and he prayed on a small mat.

حَدَّثَنَا يَحْيَى بْنُ يَحْيَى التَّمِيمِيُّ، أَخْبَرَنَا خَالِدُ بْنُ عَبْدِ اللَّهِ، ح وَحَدَّثَنَا أَبُو بَكْرِ بْنُ أَبِي شَيْبَةَ، قَالَ حَدَّثَنَا عَبَّادُ بْنُ الْعَوَّامِ، كِلاَهُمَا عَنِ الشَّيْبَانِيِّ، عَنْ عَبْدِ اللَّهِ بْنِ شَدَّادٍ، قَالَ حَدَّثَتْنِي مَيْمُونَةُ، زَوْجُ النَّبِيِّ صلى الله عليه وسلم قَالَتْ كَانَ رَسُولُ اللَّهِ صلى الله عليه وسلم يُصَلِّي وَأَنَا حِذَاءَهُ وَرُبَّمَا أَصَابَنِي ثَوْبُهُ إِذَا سَجَدَ وَكَانَ يُصَلِّي عَلَى خُمْرَةٍ ‏.‏

Abu Sa'id al-Khudri reported that he went to the Messenger of Allah (ﷺ) and found him observing prayer on a mat and prostrating on that.

وَحَدَّثَنَا أَبُو بَكْرِ بْنُ أَبِي شَيْبَةَ، وَأَبُو كُرَيْبٍ قَالاَ حَدَّثَنَا أَبُو مُعَاوِيَةَ، ح وَحَدَّثَنِي سُوَيْدُ بْنُ سَعِيدٍ، قَالَ حَدَّثَنَا عَلِيُّ بْنُ مُسْهِرٍ، جَمِيعًا عَنِ الأَعْمَشِ، ح وَحَدَّثَنَا إِسْحَاقُ بْنُ إِبْرَاهِيمَ، - وَاللَّفْظُ لَهُ - أَخْبَرَنَا عِيسَى بْنُ يُونُسَ، حَدَّثَنَا الأَعْمَشُ، عَنْ أَبِي سُفْيَانَ، عَنْ جَابِرٍ، قَالَ حَدَّثَنَا أَبُو سَعِيدٍ الْخُدْرِيُّ، أَنَّهُ دَخَلَ عَلَى رَسُولِ اللَّهِ صلى الله عليه وسلم فَوَجَدَهُ يُصَلِّي عَلَى حَصِيرٍ يَسْجُدُ عَلَيْهِ ‏.‏