Devibhagavatapurana 3.17.24

3.17.24

taptvā bahūni varṣāṇi tapo ghoraṃ mahāvane |
ṛṣitvaṃ prāpa gādheyastyaktvā kṣātraṃ vidhiṃ punaḥ ||

Performing penance and tapasyâ, very hard indeed, in the great forest, Vis'vâmitra, the son of Gâdhi, succeeded at last in becoming a Risi and then he renounced his Ksattriya Dharma.