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 c

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 ‏.‏
Reference : Sahih Muslim 660c
In-book reference : Book 5, Hadith 336
USC-MSA web (English) reference : Book 4, Hadith 1391
  (deprecated numbering scheme)