Language:
كتاب الصلاة
8  
Prayers (Salat)
(20)
Chapter: To offer As-Salat (the prayers) on the Hasir (a mat that is made of the leaves of date-palm trees and is as long as or longer than a man's stature
(20)
باب الصَّلاَةِ عَلَى الْحَصِيرِ
Sahih al-Bukhari 380

Narrated 'Is-haq:

Anas bin Malik said, "My grandmother Mulaika invited Allah's Messenger (ﷺ) for a meal which she herself had prepared. He ate from it and said, 'Get up! I will lead you in the prayer.' " Anas added, "I took my Hasir, washed it with water as it had become dark because of long use and Allah's Messenger (ﷺ) stood on it. The orphan (Damira or Ruh) and I aligned behind him and the old lady (Mulaika) stood behind us. Allah's Messenger (ﷺ) led us in the prayer and offered two rak`at and then left."

حَدَّثَنَا عَبْدُ اللَّهِ، قَالَ أَخْبَرَنَا مَالِكٌ، عَنْ إِسْحَاقَ بْنِ عَبْدِ اللَّهِ بْنِ أَبِي طَلْحَةَ، عَنْ أَنَسِ بْنِ مَالِكٍ، أَنَّ جَدَّتَهُ، مُلَيْكَةَ دَعَتْ رَسُولَ اللَّهِ صلى الله عليه وسلم لِطَعَامٍ صَنَعَتْهُ لَهُ، فَأَكَلَ مِنْهُ ثُمَّ قَالَ ‏ "‏ قُومُوا فَلأُصَلِّ لَكُمْ ‏"‏‏.‏ قَالَ أَنَسٌ فَقُمْتُ إِلَى حَصِيرٍ لَنَا قَدِ اسْوَدَّ مِنْ طُولِ مَا لُبِسَ، فَنَضَحْتُهُ بِمَاءٍ، فَقَامَ رَسُولُ اللَّهِ صلى الله عليه وسلم وَصَفَفْتُ وَالْيَتِيمَ وَرَاءَهُ، وَالْعَجُوزُ مِنْ وَرَائِنَا، فَصَلَّى لَنَا رَسُولُ اللَّهِ صلى الله عليه وسلم رَكْعَتَيْنِ ثُمَّ انْصَرَفَ‏.‏
Reference : Sahih al-Bukhari 380
In-book reference : Book 8, Hadith 32
USC-MSA web (English) reference : Vol. 1, Book 8, Hadith 377
  (deprecated numbering scheme)