And the explanation of the evidence that performing istinja (cleaning oneself) with only stones without using water is also sufficient.

Sayyiduna Salman (may Allah be pleased with him) narrates that a polytheist said to him—and the polytheists used to mock him—I see that your companion (Muhammad, peace and blessings be upon him) teaches you (everything), even the manner of relieving yourselves. Sayyiduna Salman replied: Yes, he (peace and blessings be upon him) has commanded us that (when relieving ourselves) we should not face the Qiblah, nor use our right hand for cleaning, nor be content with less than three stones, and that there should not be dung or bone among them. In the narration of Duraqi, the words are as follows «‏‏‏‏قَالَ بَعضُ المُشرِکِینَ لِسَلمَانَ» ‏‏‏‏ "A polytheist said to Hazrat Salman (may Allah be pleased with him)."