Allah said,

﴿وَإِن كُنتُم مَّرْضَى أَوْ عَلَى سَفَرٍ أَوْ جَآءَ أَحَدٌ مِّنْكُم مِّنَ الْغَائِطِ أَوْ لَـمَسْتُمُ النِّسَآءَ فَلَمْ تَجِدُواْ مَآءً فَتَيَمَّمُواْ صَعِيداً طَيِّباً فَامْسَحُواْ بِوُجُوهِكُمْ وَأَيْدِيكُمْ مِّنْهُ﴾

(But if you are ill or on a journey or any of you comes from the Gha'it (toilet), or you have touched women and you find no water, then perform Tayammum with clean earth and rub therewith your faces and hands.) We discussed all of this in Surat An-Nisa', and thus we do not need to repeat it here. We also mentioned the reason behind revealing this Ayah. Yet, Al-Bukhari mentioned an honorable Hadith here specifically about the Tafsir of this noble Ayah. He recorded that `A'ishah said, "Upon returning to Al-Madinah, a necklace of mine was broken (and lost) in Al-Bayda' area. Allah's Messenger stayed there and went to sleep with his head on my lap. Abu Bakr (`A'ishah's father) came and hit me on my flank with his hand saying, `You have detained the people because of a necklace' So I wished I were dead because (I could not move) the Messenger was sleeping on my lap and because of the pain Abu Bakr caused me. Allah's Messenger got up when dawn broke and there was no water. So Allah revealed,

﴿يَـأَيُّهَا الَّذِينَ ءَامَنُواْ إِذَا قُمْتُمْ إِلَى الصَّلوةِ فاغْسِلُواْ وُجُوهَكُمْ﴾

(O you who believe! When you stand (intend) to offer As-Salah (the prayer), then wash your faces) iuntil the end of the Ayah. Usayd bin Al-Hudayr said, `O the family of Abu Bakr! Allah has blessed the people because of you. Therefore, you are only a blessing for the people.'' Allah said,

﴿مَا يُرِيدُ اللَّهُ لِيَجْعَلَ عَلَيْكُم مِّنْ حَرَجٍ﴾

(Allah does not want to place you in difficulty,) This is why He made things easy and lenient for you. This is why He allowed you to use Tayammum when you are ill and when you do not find water, to make things comfortable for you and as mercy for you. Allah made Tayammum in place of Wudu', and Allah made it the same as ablution with water for the one who it is legitimate for, except for certain things, as we mentioned before. For example; Tayammum only involves one strike with the hand on the sand and wiping the face and hands. Allah said,

﴿وَلَـكِن يُرِيدُ لِيُطَهِّرَكُمْ وَلِيُتِمَّ نِعْمَتَهُ عَلَيْكُمْ لَعَلَّكُمْ تَشْكُرُونَ﴾

(but He wants to purify you, and to complete His favor on you that you may be thankful.) for His bounties on you, such as His easy, kind, merciful, comfortable and lenient legislation.