Shiva Purana
मम भक्तं यदा कश्चित्पीडयत्यतिदारुणः ॥ तदाहं तस्य रक्षार्थं दुष्टं हन्मि न संशयः ॥ १२ ॥
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