Al-Maaida 5:6

O you who believe, when you rise up for prayer, wash your faces, and your hands up to the elbows; wipe over your heads; and wash your feet up to the ankles. If you are in a state of major impurity, cleanse yourselves [by taking a bath]. But if you are ill, on a journey, or have relieved yourselves, or had sexual contact[11] with women and find no water, then purify yourselves with clean earth[12], and wipe your faces and hands therewith. Allah does not want to impose hardship on you, rather He wants to purify you and complete His favor upon you, so that you may be grateful.

[11] i.e., had sexual intercourse or seminal discharge.
[12] This is the act of dry ablution or tayammum.

O you who have believed, when you rise to [perform] prayer, wash your faces and your forearms to the elbows and wipe over your heads and wash your feet to the ankles. And if you are in a state of janābah,[245] then purify yourselves. But if you are ill or on a journey or one of you comes from the place of relieving himself or you have contacted women[246] and do not find water, then seek clean earth and wipe over your faces and hands with it. Allāh does not intend to make difficulty for you, but He intends to purify you and complete His favor upon you that you may be grateful.

[245] See footnote to 4:43.
[246] i.e., had sexual intercourse.

6. O you who believe! When you intend to offer As-Salât (the prayer), wash your faces and your hands (forearms) up to the elbows, rub (by passing wet hands over) your heads, and (wash) your feet up to ankles[3]. If you are in a state of Janâba (i.e. after a sexual discharge), purify yourselves (bathe your whole body). But if you are ill or on a journey, or any of you comes after answering the call of nature, or you have been in contact with women (i.e. sexual intercourse), and you find no water, then perform Tayammum with clean earth and rub therewith your faces and hands.[4] Allâh does not want to place you in difficulty, but He wants to purify you, and to complete His Favour to you that you may be thankful.

[3] (V.5:6) The superiority of ablution. And Al-Ghurr-ul Muhajjalûn (the parts of the body of the Muslims washed in ablution will shine on the Day of Resurrection and the angels will call them by that name) from the traces of ablution.
Narrated Nu‘aim Al-Mujmir: Once I went up the roof of the mosque along with Abu Hurairah رضي الله عنه. He performed ablution and said, "I heard the Prophet صلى الله عليه وسلم saying, ‘On the Day of Resurrection, my followers will be called Al-Ghurr-ul-Muhajjalûn from the traces of ablution and whoever can increase the area of his radiance* should do so (by performing ablution in the most perfect manner).’ " (Sahih Al-Bukhâri, Vol.1, Hadîth No.138).
*The Prophet صلى الله عليه وسلم did not increase the area more than what is washed of the body parts while doing ablution as Allâh ordered to be washed in the Qur’ân. [For details about Wudu (ablution), see Sahih Al-Bukhâri, Vol.1, (The Book of Ablution)].
[4] (V.5:6) Strike your hands on the earth and then pass the palm of each on the back of the other and then blow off the dust from them and then pass (rub) them on your face: this is called Tayammum

O ye who believe! When ye rise up for prayer, wash you faces, and your hands up to the elbows, and lightly rub your heads and (wash) your feet up to the ankles. And if ye are unclean, purify yourselves. And if ye are sick or on a journey, or one of you cometh from the closet, or ye have had contact with women, and ye find not water, then go to clean, high ground and rub your faces and your hands with some of it. Allah would not place a burden on you, but He would purify you and would perfect His grace upon you, that ye may give thanks.