E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
The Koran says, at the judgment day everyone will be weighed in the scales of the archangel Gabriel. His good deeds will be put in the scale called Light, and his evil ones in the scale called Darkness; after which they will have to cross the bridge Al Serat, not wider than the edge of a scimitar. The faithful will pass over in safety, but the rest will fall into the dreary realms of Jehennam.