Praise be to Allaah.
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.
I’laam al-Musaafireen bi Ba’d Aadaab wa Ahkaam al-Safar wa maa yakhuss al-Mallaaheen al-Jawwiyyeen by Shaykh Muhammad ibn Saalih al-‘Uthaymeen, p. 10