Thor's daughter, Þrúðr, was promised in marriage to Alvíss. Thor was unhappy with the match however, so he devised a plan. He told Alvíss that, because of his small height, he had to prove his wisdom. Alvíss agreed, but Thor made his tests last until dawn, when Alviss, because he was a dwarf, was turned to stone on being exposed to the sunlight.
Alvissmol, the poem containing most of the information on Alviss
Lindow, John (October 1994), "Thor's 'Hamarr'", The Journal of English and Germanic Philology, 93 (4): 485–503, JSTOR27711059, accessed 13 May 2015.