Sahih Muslim
Sahih Muslim 660 b
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
Arabic hadith text
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 وسلمصَلَّى بِهِ وَبِأُمِّهِ أَوْ خَالَتِهِ . قَالَ فَأَقَامَنِي عَنْ يَمِينِهِ وَأَقَامَ الْمَرْأَةَ خَلْفَنَا .
Translation
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.