Shiva Purana
अपसर्प्पन्त्विति प्रोच्य प्रणवं तदनंतरम् ॥ अस्त्राय फडिति प्रोच्य पार्ष्णिघातत्रयेण तु ॥ ५०॥
After saying 'Let them withdraw' he chanted the oṁkāra He said 'Phadi' to the weapon and struck him three times on the heel.
english translation
apasarppantviti procya praNavaM tadanaMtaram ॥ astrAya phaDiti procya pArSNighAtatrayeNa tu ॥ 50॥
hk transliteration by Sanscript