The Book of Clothes and Adornment
حَدَّثَنَا أَبُو بَكْرِ بْنُ أَبِي شَيْبَةَ، حَدَّثَنَا عَبْدَةُ بْنُ سُلَيْمَانَ، عَنْ هِشَامِ بْنِ عُرْوَةَ، عَنْ أَبِيهِ، عَنْ عَائِشَةَ، قَالَتْ كَانَ وِسَادَةُ رَسُولِ اللَّهِ صلى الله عليه وسلم الَّتِي يَتَّكِئُ عَلَيْهَا مِنْ أَدَمٍ حَشْوُهَا لِيفٌ .A'isha reported that the pillow on which Allah's Messenger (ﷺ) reclined was of leather stuffed with palm fibre
From Sahih Muslim, whose reports the scholars accept as authentic.