Kaṁsa thought: What is my duty now? The Supreme Lord, who knows His purpose will not give up His prowess. Devakī is a woman, she is my sister, and moreover she is now pregnant. If I kill her, my reputation, opulence and duration of life will certainly be vanquished.
Srimad Bhagavata Purana
श्रीमद्भागवतमहापुराणम्
मूल श्लोकः
किमद्य तस्मिन् करणीयमाशु मे यदर्थतन्त्रो न विहन्ति विक्रमम् । स्त्रियाः स्वसुर्गुरुमत्या वधोऽयं यशः श्रियं हन्त्यनुकालमायुः
kimadya tasmin karaṇīyamāśu me yadarthatantro na vihanti vikramam | striyāḥ svasurgurumatyā vadho'yaṃ yaśaḥ śriyaṃ hantyanukālamāyuḥ
SB 10.2.21