It should be understood that although water is the best means to remove impurities and cleanse oneself, it is permissible, when water is not available or cannot be used, to use any other clean substance for the purpose of purification after relieving oneself. Istinja’ is the Islamic term for the action of using water to clean oneself after urinating and/or defecating.
In his well-known book, Fiqh As-Sunnah, Sheikh Sayyed Sabiq states the following:
“After answering the call of nature, one should cleanse his private parts. To do so, he can use a rock, stone or any other pure substance. One may use only water to clean the area, or any combinations of purifying agents.
`A’ishah (may Allah be pleased with her) reported that the Prophet (peace and blessings be upon him) said, “When one of you goes to relieve himself, he should clean himself with three stones.” (Reported by Ahmad, An-Nasa’i, Abu Dawud and Ad-Daraqutni).
Anas related that the Prophet (peace and blessings be upon him) would enter the privy, and that Anas and another boy would carry the water container and a spear for him. The Prophet would clean himself with water. (Reported by Al-Bukhari and Muslim)”
Sheikh Ahmad Kutty also states:
“Islam teaches us to use water for purification after relieving oneself whenever and wherever possible. However, in cases where water is not available, or water becomes scarce, or unusable because of sickness or other valid reasons, we are allowed to have recourse to pebbles, leaves, paper or any clean substance, other than bones or animal excrement, for wiping oneself clean of the filth as much as possible. While cleaning ourselves in this way, we must ensure that the entire surface is wiped clean without leaving any discernible trace of filth.
Scholars of Islam have unanimously decided that, for purposes of purification after relieving oneself, clean toilet paper is as good as pebbles or leaves when water is not readily available or cannot be used.
It is important for us to remember that the use of pebbles or clean toilet paper in this manner is a dispensation or concession (ruksah) that Allah has provided for us, and, as the Prophet (peace and blessings be upon him) has taught us, “Allah loves His servants to make use of His dispensations”. We must also remember Allah’s words in the Qur’an: “He has not placed any hardship for you in your religion.” (Al-Hajj: 78).
The Prophet (peace and blessings be upon him) also said: “This religion of ours is easy and simple to practice; if you make it hard upon yourself, you will be defeated by it.” (Sahih al-Bukhari)
Accordingly, one can make use of this dispensation and purify oneself in this way. But one is not allowed to let the time of salah elapses without performing it in its due time. Salah has certain times to be performed in and they cannot be missed.