Skandapurana 5.237.31

5.237.31

etaddhi tapaso mūlaṃ yadetanmanasastyajet ..
tyakteṣveteṣu sarveṣu para brahmamayo bhavet .. 31 ..

For this is the root of austerity, that one should cast this out from the mind. / When all these are abandoned, one becomes composed of the supreme Brahman.