The Book of Prayers
حَدَّثَنَا مُحَمَّدُ بْنُ عَبْدِ اللَّهِ بْنِ نُمَيْرٍ، حَدَّثَنَا عَبْدُ اللَّهِ بْنُ يَزِيدَ، أَخْبَرَنَا حَيْوَةُ، عَنْ أَبِي الأَسْوَدِ، مُحَمَّدِ بْنِ عَبْدِ الرَّحْمَنِ عَنْ عُرْوَةَ، عَنْ عَائِشَةَ، أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم سُئِلَ فِي غَزْوَةِ تَبُوكَ عَنْ سُتْرَةِ الْمُصَلِّي فَقَالَ " كَمُؤْخِرَةِ الرَّحْلِ " .A'isha reported:The Messenger of Allah (ﷺ) was asked in the expedition of Tabuk about the sutra the worshipper; he said: Like the back of the saddle
From Sahih Muslim, whose reports the scholars accept as authentic.