Allah Subhana wa Ta'ala has described on the Quran, Surah 5, Section 2, Verses 6.

"O ye who believe! When ye rise up for prayer, wash your face, 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. "