To offer As-Salat (the prayer) using a Harba (a short spear) (as a Sutra)

Sahih al-Bukhari · Book 8 · Hadith 498

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.‏

Narrated `Abdullah: The Prophet (ﷺ) used to get a Harba planted in front of him (as a Sutra) and pray behind it.