It is narrated from Yasar bin Numayr, the freed slave of Umar, that when Sayyiduna Umar (may Allah be pleased with him) urinated he would say: Give me something with which to clean myself. The narrator said: I would hand him a piece of wood or a stone, or he would come to a wall and wipe himself against it, or touch the ground, and he would not wash it.
This is the most authentic and the highest of what has been narrated in this chapter.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 540