Sahih al-Bukhari, Volume 1, Book 9, Hadith 477 (USC-MSA) ⓘ
Narrated `Abdullah: The Prophet used to get a Harba planted in front of him (as a Sutra) and pray behind it.
حَدَّثَنَا مُسَدَّدٌ، قَالَ حَدَّثَنَا يَحْيَى، عَنْ عُبَيْدِ اللَّهِ، أَخْبَرَنِي نَافِعٌ، عَنْ عَبْدِ اللَّهِ، أَنَّ النَّبِيَّ صلى الله عليه وسلم كَانَ يُرْكَزُ لَهُ الْحَرْبَةُ فَيُصَلِّي إِلَيْهَا.
also referenced under: Book 8, Hadith 145 (In-Book) & Hadith 498 (DarusSalam)