Skandapurana 5.142.15

5.142.15

brahmacaryaṃ tapomūlaṃ yataḥ saṃkīrtitaṃ dvijaiḥ ..
tasyābhāvātparikleśaḥ kevalaṃ na phalaṃ vrate .. 15 ..

For celibacy is proclaimed by brahmins to be the root of austerity; / in its absence, there is mere distress, without fruit in the vow.” (15)