Skandapurana 6.3.118.18

6.3.118.18

ārdravāsāstu hemante cacāra vipulaṃ tapaḥ .
evaṃ tu tapatastasya indrasya viditātmanaḥ .. 118.18 ..

and in winter wearing wet clothes, he practiced vast austerity. / While Indra, whose self was known, was thus practicing austerity,