Shiva Purana
सिद्धमन्त्रो ऽप्यदृष्टेन प्रबलेन तु केनचित् ॥ प्रतिबन्धफलं कर्म न कुर्यात्सहसा बुधः ॥ ४ ॥
A learned and sensible devotee, even after the mantra has been achieved, shall not haphazardly perform any rite the fruit whereof has been thwarted by some unseen powerful obstacle.
english translation
siddhamantro 'pyadRSTena prabalena tu kenacit ॥ pratibandhaphalaM karma na kuryAtsahasA budhaH ॥ 4 ॥
hk transliteration by Sanscript