بِسْمِ اللَّهِ الرَّحْمَٰنِ الرَّحِيمِ
The procedure of ‘Wadu’/ablution is laid down in ayat 6 of sura ‘Maida’:
5:6 يَا أَيُّهَا الَّذِينَ آمَنُوا إِذَا قُمْتُمْ إِلَى الصَّلَاةِ فَاغْسِلُوا وُجُوهَكُمْ وَأَيْدِيَكُمْ إِلَى الْمَرَافِقِ وَامْسَحُوا بِرُءُوسِكُمْ وَأَرْجُلَكُمْ إِلَى الْكَعْبَيْنِ ۚ وَإِن كُنتُمْ جُنُبًا فَاطَّهَّرُوا ۚ وَإِن كُنتُم مَّرْضَىٰ أَوْ عَلَىٰ سَفَرٍ أَوْ جَاءَ أَحَدٌ مِّنكُم مِّنَ الْغَائِطِ أَوْ لَامَسْتُمُ النِّسَاءَ فَلَمْ تَجِدُوا مَاءً فَتَيَمَّمُوا صَعِيدًا طَيِّبًا فَامْسَحُوا بِوُجُوهِكُمْ وَأَيْدِيكُم مِّنْهُ ۚ مَا يُرِيدُ اللَّهُ لِيَجْعَلَ عَلَيْكُم مِّنْ حَرَجٍ وَلَٰكِن يُرِيدُ لِيُطَهِّرَكُمْ وَلِيُتِمَّ نِعْمَتَهُ عَلَيْكُمْ لَعَلَّكُمْ تَشْكُرُونَ
“O’ you people who believe! when you stand for salah/prayer, wash your faces and your hands to the elbows; rub your heads and (wash) your feet to the ankles. And if you are in a state of stranger, so purify yourselves. And if you are ill or on a journey, or one of you come from call of nature, or you have been in contact with women, and find no water, so you take for yourselves clean sand/good high land, so rub your faces and hands from it. Allah does not wish to place you in difficulty but to make you clean, and to complete His favor on you, that you may be grateful.”
In ‘Wadu’/ablution you have to to wash your faces, wash hands upto your elbows, rub your head and (wash) your feet upto the ankles.
Washing of feet is implied by the Fatha (Zabar) on the La of Arju la kum وَأَرْجُلَكُمْ (your feet) which connects it to the verb فَاغْسِلُوا (wash) .
Please verify in the same ayat above that, when وُجُوهَكُمْ (your faces) and أَيْدِيَكُمْ (your hands) are used with فَاغْسِلُوا (Wash) there is a Fatha/Zabar on them. (normal case of object of the verb with Fatha, indicating ‘faces’ and ‘hands’ in the sentence as the objects of the verb ‘wash’)
However, when بِوُجُوهِكُمْ (your faces) and أَيْدِيكُم (your hands) are used with فَامْسَحُوا (rub) they are with Kasra/ Zair. (In the below example with ‘F’amsahu/rub’, due to the particle ‘Ba’ used with faces (bi-wujuhikum), the object of the verb (your faces) is with Kasra instead of Fatha. The same Kasra is used in Aidikum/hands (instead of Fatha) indicates that both are connected to the verb F’amsahu. Therefore if in وَامْسَحُوا بِرُءُوسِكُمْ وَأَرْجُلَكُمْ, Arjulakum (your feet, which is the object, were connected with the verb ‘Wamsau/rub’, then it would have been with Kasra.
فَاغْسِلُوا وُجُوهَكُمْ وَأَيْدِيَكُمْ
فَامْسَحُوا بِوُجُوهِكُمْ وَأَيْدِيكُم
Worth mentioning is an Ayat 56:79 which is normally used to justify that its obligation to do the Wadu/Ablution before you can touch the Book.
56:79 لَّا يَمَسُّهُ إِلَّا الْمُطَهَّرُونَ
“None can touch/grasp it except those pure/clean”
Unless you have gotten rid of contamination of idols and preconceived notions/stories, you will not be able to grasp the sprit of the Book. The understanding will start coming after approaching the Book with a pure heart. Making Wadu obligatory before touching the Book is tantamount to creating an additional hurdle for people to resort to the Book.