Shiva Purana
तथापि नैव क्षुद्रेषु फलेषु प्रति योगिषु ॥ सहसा विनियुंजीत तस्मादेष महाबलः ॥ ७५ ॥
Still this mantra shall not be used for the trivial benefits or against insignificant opponents. Then alone this is very efficacious.
english translation
tathApi naiva kSudreSu phaleSu prati yogiSu ॥ sahasA viniyuMjIta tasmAdeSa mahAbalaH ॥ 75 ॥
hk transliteration by Sanscript