Ruling on sufficiency of using tissues and the like for istinja'

Question:
From 'Abd al-'Aziz ibn 'Abd Allah ibn Baz to his honorable sister in Allah, K. 'A. Q., at the Rehabilitation Hospital in al-Ta'if, may Allah guide her to all good. Amen.
Peace be upon you, and Allah's mercy and blessings. As for what follows:
Your letter containing the eight questions has reached me, and the text of the third question and its answer is as follows. Regarding the third, which is: your inability to perform istinja' with water due to illness?

Answer:
The answer is: It suffices for you to clean yourself by performing istinja' with pure tissues and the like, such as stones or wood, three times or more, until the impurity is removed from the front and the back. Less than three times is not sufficient. If three times are not enough, it is obligatory to increase beyond three until the back and the front are purified from the impurity. This suffices in place of water. May Allah heal you and the Muslims from all evil.