كتاب الْمَسَاجِدِ وَمَوَاضِعِ الصَّلاَةِ
5  
The Book of Mosques and Places of Prayer
(48)
Chapter: 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
(48)
باب جَوَازِ الْجَمَاعَةِ فِي النَّافِلَةِ وَالصَّلاَةِ عَلَى حَصِيرٍ وَخُمْرَةٍ وَثَوْبٍ وَغَيْرِهَا مِنَ الطَّاهِرَاتِ
Sahih Muslim 660 a

Thabit reported on the authority of Anas:

The Apostle of Allah (ﷺ) came to us and there was none in our house but I, my mother and my aunt Umm Haram. He (the Holy 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 Holy 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 ‏"‏ ‏.‏
Reference : Sahih Muslim 660a
In-book reference : Book 5, Hadith 334
USC-MSA web (English) reference : Book 4, Hadith 1389
  (deprecated numbering scheme)