Sahih Bukhari Volume 001, Book 007, Hadith Number 344.
Hadith Section/Book: Sahih Bukhari Sahih Bukhari Book 07. Rubbing Hands and Feet With Dust (Tayammum)
Narated By 'Imran bin Husain Al-Khuza'i : Allah's Apostle saw a person sitting aloof and not praying with the people. He asked him, "O so and so! What prevented you from offering the prayer with the people?" He replied, "O Allah's Apostle! I am Junub and there is no water." The Prophet said, "Perform Tayammum with clean earth and that will be sufficient for you."