Narrated Anas (Radi-Allahu ‘anhu):
That the people of Makkah requested Allah’s Apostle (Sallallahu ‘Alaihi Wa Sallam) to show them a miracle, and so he showed them the splitting of the moon.
Bukhari Vol. 4 : No. 831
[Photograph of Lunar rilles are sometimes used as “proof” of the moon splitting miracle. (more images=http://wikiislam.net/wiki/Moon_Split_Images#Images_of_Rilles)]