The Messenger of Allah ﷺ said, "The earth has been made for me a means of purification and a place of prayer."
قال رسول الله ﷺ: جعلت لي الأرض طهورا ومسجدا.
Abu Dawud (498) narrated it from Uthman bin Abu Shayba, who said, "Jareer narrated to us, from Amash, from Mujahid bin Jabr, from Ubaydullah bin Umar Al-Laythi, from Abu Dharr," and he mentioned the hadith. Its isnad is sahih. Hakim (2/424) also narrated it at length through the route of Amash with the same chain... and he said, "It meets the standard of the two sheikhs, though they did not narrate it in this wording, but rather narrated scattered phrases from the hadith."