Skandapurana 7.13.p58

7.13.p58

yathā tvasya svasāpīyaṃ naiva52 bādhāṃ53 kariṣyati .
tathā caratvayaṃ ghoraṃ tapaḥ paramaduścaram ..69. .
yūyaṃ ca ṛṣibhiḥ sārdhamihaiva susamāhitāḥ .
puraścaraṇamavyagrāḥ kurudhvaṃ madanujñayā . .8.122.70 ..

Yet, so that this sister of his does not cause any affliction,
let him perform severe austerity, exceedingly hard to practice.
And you, together with the seers, right here, deeply concentrated,
perform the preparatory rite untroubled, by my command.”