Allah said,

﴿وَإِنْ كُنتُم مَّرْضَى أَوْ عَلَى سَفَرٍ أَوْ جَآءَ أَحَدٌ مِّنْكُمْ مِّن الْغَآئِطِ أَوْ لَـمَسْتُمُ النِّسَآءَ فَلَمْ تَجِدُواْ مَآءً فَتَيَمَّمُواْ صَعِيداً طَيِّباً﴾

(and if you are ill, or on a journey, or one of you comes from the Gha'it (toilet), or from Lamastum (touching) women, but you do not find water, then perform Tayammum with clean earth, rubbing your face and hands. Truly, Allah is Ever Oft-Pardoning, Oft-Forgiving.) As for the type of illness which would allow Tayammum, it is an illness that one fears would be aggravated by using water, which could be detrimental to a part of the body, or when doing so would prolong an illness. Some scholars said that any type of illness warrants Tayammum, because of the general indications of the Ayah. As for travelling on a journey, it is known, regardless of its length. Allah then said,

﴿أَوْ جَآءَ أَحَدٌ مِّنْكُمْ مِّن الْغَآئِطِ﴾

(or comes from the Gha'it). The Gha'it is, literally, the flat land, and this part of the Ayah refers to the minor impurity. Allah then said,

﴿أَوْ لَـمَسْتُمُ النِّسَآءَ﴾

(or you Lamastum women), which was recited Lamastum and Lamastum, referring to sexual intercourse. For instance, Allah said in another Ayah,

﴿وَإِن طَلَّقْتُمُوهُنَّ مِن قَبْلِ أَن تَمَسُّوهُنَّ وَقَدْ فَرَضْتُمْ لَهُنَّ فَرِيضَةً فَنِصْفُ مَا فَرَضْتُمْ﴾

(And if you divorce them before you have touched them, and you have appointed unto them the dowry, then pay half of that) ﴿2:237﴾, and,

﴿يأَيُّهَا الَّذِينَ ءَامَنُواْ إِذَا نَكَحْتُمُ الْمُؤْمِنَـتِ ثُمَّ طَلَّقْتُمُوهُنَّ مِن قَبْلِ أَن تَمَسُّوهُنَّ فَمَا لَكُمْ عَلَيْهِنَّ مِنْ عِدَّةٍ تَعْتَدُّونَهَا﴾

(O you who believe! When you marry believing women, and then divorce them before you have touched them, no `Iddah (period of waiting) have you to count in respect of them) ﴿33:49﴾. Ibn Abi Hatim recorded that Ibn `Abbas said that Allah's statement,

﴿أَوْ لَـمَسْتُمُ النِّسَآءَ﴾

(or Lamastum women) refers to sexual intercourse. It was reported that `Ali, Ubayy bin Ka`b, Mujahid, Tawus, Al-Hasan, `Ubayd bin `Umayr, Sa`id bin Jubayr, Ash-Sha`bi, Qatadah and Muqatil bin Hayyan said similarly. Allah said,

﴿فَلَمْ تَجِدُواْ مَآءً فَتَيَمَّمُواْ صَعِيداً طَيِّباً﴾

(but you do not find water,them perform Tayammum with clean earth,) In the Two Sahihs, it is recorded that `Imran bin Husayn said, إن رسول الله صلى الله عليه وسلّم رأى رجلا معتزلا لم يصل في القوم فقال:

«يَا فُلَانُ مَا مَنَعَكَ أَنْ تُصَلِّيَ مَعَ الْقَوْمِ، أَلَسْتَ بِرَجُلٍ مُسْلِمٍ؟»

قال: بلى، يا رسول الله ولكن أصابتني جنابة ولا ماء، قال:

«عَلَيْكَ بِالصَّعِيدِ، فَإِنَّهُ يَكْفِيك»

(Allah's Messenger saw a person sitting away from the people and not praying with them. He asked him, `O so-and-so! What prevented you from offering the prayer with the people, are not you Muslim' He replied, `Yes, O Allah's Messenger! I am Junub and there is no water.' The Prophet said, `Perform Tayammum with clean earth and that will be sufficient for you.') The linguistic meaning of Tayammum is to intend, as Arabs say, "May Allah Tayammamaka (direct at you) His care.'' `Clean earth' means dust. In his Sahih, Muslim recorded that Hudhayfah bin Al-Yaman said that the Messenger of Allah said,

«فُضِّلْنَا عَلَى النَّاسِ بِثَلَاثٍ: جُعِلَتْ صُفُوفُنَا كَصُفُوفِ الْمَلَائِكَةِ، وَجُعِلَتْ لَنَا الْأَرْضُ كُلُّهَا مَسْجِدًا، وَجُعِلَتْ تُرْبَتُهَا لَنَا طَهُورًا، إِذَا لَمْ نَجِدِ الْمَاء»

(We were given preference over people in three things. Our lines (in prayer) were arranged in rows to resemble the rows of the angels, all of the earth was made a Masjid for us, and its dust was made clean for us when there is no water.) The Messenger mentioned the favor of making dust a purifyer for us, and if there were any other substance to replace it for Tayammum, he would have mentioned it. Imam Ahmad and the collectors of Sunan, with the exception of Ibn Majah, recorded that Abu Dharr said that the Messenger of Allah said,

«الصَّعِيدُ الطَّيِّبُ طَهُورُ الْمُسْلِمِ، وَإِنْ لَمْ يَجِدِ الْمَاءَ عَشْرَ حِجَجٍ، فَإِذَا وَجَدَهُ فَلْيُمِسَّهُ بَشَرَتَهُ، فَإِنَّ ذَلِكَ خَيْر»

(Clean earth is pure for the Muslim, even if he does not find water for ten years. When he finds water, let him use it for his skin, for this is better.) At-Tirmidhi said, "Hasan Sahih''. Allah's statement,

﴿فَامْسَحُواْ بِوُجُوهِكُمْ وَأَيْدِيَكُمْ﴾

(rubbing your faces and hands (Tayammum)) indicates that Tayammum is a substitute for normal ablution, not that it involves cleaning the parts that normal ablution does. Therefore, it is sufficient in Tayammum to just wipe the face and hands, as the consensus concurs. The face and hands are wiped with one strike on the sand in this case, as Imam Ahmad recorded that `Abdur-Rahman bin Abza said that a man came to `Umar and asked him, "I am Junub, but there is no water.'' `Umar said, "Then, do not pray.'' `Ammar said, "Do you not remember, O Leader of the Faithful! You and I were on a military expedition when we became Junub and did not find water. You did not pray, but I rolled myself in the sand and then prayed. When we went back to the Prophet, we mentioned to him what had happened. He said to me, S

«إِنَّمَا كَانَ يَكْفِيك»

(This would have been sufficient for you), and the Prophet stroked his hand on the earth once, blew into it and wiped his face and hands.'' The Muslim Ummah, rather than all other nations, was favored with the allowance of Tayammum. In the Two Sahihs, it is recorded that Jabir bin `Abdullah said that the Messenger of Allah said,

«أُعْطِيتُ خَمْسًا لَمْ يُعْطَهُنَّ أَحَدٌ قَبْلِي: نُصِرْتُ بِالرُّعْبِ مَسِيرَةَ شَهْرٍ، وَجُعِلَتْ لِيَ الْأَرْضُ مَسْجِدًا وَطَهُورًا، فَأَيُّمَا رَجُلٍ مِنْ أُمَّتِي أَدْرَكَتْهُ الصَّلَاةُ فَلْيُصَل»

وفي لفظ:

«فَعِنْدَهُ طَهُورُهُ وَمَسْجِدُهُ، وَأُحِلَّتْ لِيَ الْغَنَائِمُ، وَلَمْ تَحِلَّ لِأَحَدٍ قَبْلِي، وَأُعْطِيتُ الشَّفَاعَةَ، وَكَانَ النَّبِيُّ يُبْعَثُ إِلى قَوْمِهِ، وَبُعِثْتُ إِلَى النَّاسِ عَامَّة»

(I have been given five things which were not given to any (Prophet) before me: Allah made me victorious with fright that covers a month's distance. The earth has been made for me (and for my followers) a place for praying and an object to perform purification with. Therefore let my followers pray wherever the time of a prayer is due - and in another narration - he will have his means of purity and his Masjid. The spoils of war have been made lawful for me and it was not made so for anyone else before me. I have been given the right of intercession (on the Day of Resurrection.) Every Prophet used to be sent to his nation exclusively, but I have been sent to all mankind.) We also mentioned the Hadith of Hudhayfah that Muslim recorded;

«فُضِّلْنَا عَلَى النَّاسِ بِثَلَاثٍ، جُعِلَتْ صُفُوفُنَا كَصُفُوفِ الْمَلَائِكَةِ، وَجُعِلَتْ لَنَا الْأَرْضُ مَسْجِدًا، وَتُرْبَتُهَا طَهُورًا، إِذَا لَمْ نَجِدِ الْمَاء»

(We were preferred with three things over people. Our lines (in prayer) were arranged in rows to resemble the rows of the angels, all of the earth was made a Masjid for us, and its dust was made clean for us when there is no water.) Allah said in this Ayah,

﴿فَامْسَحُواْ بِوُجُوهِكُمْ وَأَيْدِيَكُمْ إِنَّ اللَّهَ كَانَ عَفُوّاً غَفُوراً﴾

(rubbing your faces and hands. Truly, Allah is Ever Oft-Pardoning, Oft-Forgiving.) meaning, a part of His pardoning and forgiving is that He allows you to use Tayammum and to pray after using it when there is no water, to make things easy for you. This Ayah sanctifies the position of the prayer, it being too sacred than to be performed in a defecient manner, like in a state of drunkenness, until one becomes aware of what he is saying, or sexually impure, until he bathes (Ghusl), or after answering the call of nature, until he performs ablution. There are exceptions when one is ill or when there is no water. In this case, Allah allows us to use Tayammum, out of His mercy and kindness for His servants, and to facilitate them, all praise is due to Allah.