Skandapurana 5.244.5

5.244.5

maheśvaraśca liṃgatvaṃ kathaye'haṃ tavā'nagha ..
pūrvaṃ prajāpatirdakṣo brahmaṇoṃ'guṣṭha saṃbhavaḥ .. 5 ..'

and how Maheśvara became a liṅga, I shall tell you, O sinless one. / Formerly, the progenitor Dakṣa, who arose from the thumb of Brahmā—