Targum zu Bereschit 19:26

And his wife looked after the angel, to know what would be in the end of her father's house, for she was of the daughters of the Sedomaee; and because she sinned by salt (bemilcha) she was manifestly punished; behold, she was made a statue of salt.

And because the wife of Lot was of the children of the people of Sedom, she looked behind her, to see what would be the end of her father's house: and, behold, she was made to stand a statue of salt, until the time of the resurrection shall come, when the dead shall arise.