What is istijmaar?
Question

                What is istijmaar (lit. cleaning oneself with stones after eliminating urine or stools)? Is it proper istijmaar to clean oneself with tissues and water when on board a plane? What is the proper way to cleanse oneself?
Praise be to Allah.Istijmaar means to cleanse 
          the front or back passage of urine or stools using stones or something 
          else in their place. One of the things that may take their place is 
          tissue, but on the condition that one wipes no less than three times. 
          And one should not use things that are forbidden to be used for istijmaar 
          such as dung and bones, or things that have a kind of sanctity such 
          as food etc.  
It is permissible to do istijmaar 
          with or without water. The scholars said, it is better to use both, 
          because that is cleaner.