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)”
Elaborating more on the permissibility of using other safe methods for purifying oneself, Dr. `Abdul-Fattah `Ashoor, professor of the Exegesis of the Qur’an at Al-Azhar University, states:
“Upon answering the call of nature, one is recommended to purify himself by using water. During the Prophet’s lifetime, people used to purify themselves after answering the call of nature by stones, due to water scarcity. Stones, of course, help a bit in that aspect but some traces of impurity still normally remain. That is why water should be used. Tissues, by analogical deduction or Qiyas, take the same ruling pertaining to stones. Hence, it is allowable to use tissues for purification. However, it is preferable to use both water and tissues, or water alone, in this process.”
Sheikh Ahmad Kutty, a senior lecturer and an Islamic scholar at the Islamic Institute of Toronto, Ontario, Canada, 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 allowance (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.”
In short, clean toilet paper is quite sufficient to rid oneself of impurity for the purposes of salah and recitation, once accompanied by wudu’ (ablution) or tayammum (dry ablution).” (Source: www.muslims.ca)