Sahih Muslim 660
Sahih Muslim · Book 5: The Book of Mosques and Places of Prayer · 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
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 .
This hadith has also been narrated by Shu'ba with this chain of transmitters.