The Book of Prayers
حَدَّثَنَا أَبُو بَكْرِ بْنُ أَبِي شَيْبَةَ، وَابْنُ، نُمَيْرٍ قَالاَ حَدَّثَنَا مُحَمَّدُ بْنُ بِشْرٍ، حَدَّثَنَا عُبَيْدُ اللَّهِ، عَنْ نَافِعٍ، عَنِ ابْنِ عُمَرَ، أَنَّ النَّبِيَّ صلى الله عليه وسلم كَانَ يَرْكُزُ - وَقَالَ أَبُو بَكْرٍ يَغْرِزُ - الْعَنَزَةَ وَيُصَلِّي إِلَيْهَا . زَادَ ابْنُ أَبِي شَيْبَةَ قَالَ عُبَيْدُ اللَّهِ وَهْىَ الْحَرْبَةُ .Ibn Umar reported:The Apostle of Allah (ﷺ) set up (sutra), and Abu Bakr said: He implanted iron-tipped spear and said prayer towards its direction. Ibn Abu Shaiba made this addition to it:" Ubaidullah said that it was a spear
From Sahih Muslim, whose reports the scholars accept as authentic.