Rasendrapurana 47.77

Rasendrapurāṇa 47.77

sattvalohayormṛdukaraṇāvaśyakatā
na sattvaṃ kaṭhine sūte dehe vā kramate kvacit
tasmātsattvaṃ ca lohaṃ ca mṛduṃ kṛtvā prayojayet