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 b

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 ‏.‏
Reference : Sahih Muslim 660b
In-book reference : Book 5, Hadith 335
USC-MSA web (English) reference : Book 4, Hadith 1390
  (deprecated numbering scheme)