The story
After a Sri Lankan Muslim legend that the seeming indentation on the mountain is a footprint left by Adam, who were forced to stand on one leg for a thousand years as penance after being expelled from Eden; a modification of the older Buddhist tradition that it is a footprint of the Buddha. In the less common Syriac Christian version of the legend it is said to made by the apostle Thomas instead.
Etymology from Wiktionary, CC BY-SA 4.0.