Shiva Purana

siva.sh/siva-purana/kotirudra-samhita/21/12

मम भक्तं यदा कश्चित्पीडयत्यतिदारुणः ।। तदाहं तस्य रक्षार्थं दुष्टं हन्मि न संशयः ।। १२ ।।

sanskrit

The promise is “If and when any terrible person harasses my devotee I shall kill that wicked person in order to save him. There is no doubt in this.”

english translation

mama bhaktaM yadA kazcitpIDayatyatidAruNaH || tadAhaM tasya rakSArthaM duSTaM hanmi na saMzayaH || 12 ||

hk transliteration by Sanscript