SB 10.1.37

śrī-vasudeva uvāca
ślāghanīya-guṇaḥ śūrair
 bhavān bhoja-yaśaskaraḥ
sa kathaṁ bhaginīṁ hanyāt
 striyam udvāha-parvaṇi
Word for word: 
śrī-vasudevaḥ uvāca — the great personality Vasudeva said; ślāghanīya-guṇaḥ — a person who possesses praiseworthy qualities; śūraiḥ — by great heroes; bhavān — your good self; bhoja-yaśaḥ-karaḥ — a brilliant star in the Bhoja dynasty; saḥ — one such as your good self; katham — how; bhaginīm — your sister; hanyāt — can kill; striyam — especially a woman; udvāha-parvaṇi — at the time of the marriage ceremony.
Translation: 
Vasudeva said: My dear brother-in-law Kaṁsa, you are the pride of your family, the Bhoja dynasty, and great heroes praise your qualities. How could such a qualified person as you kill a woman, your own sister, especially on the occasion of her marriage?
Purport: 

According to Vedic principles, a brāhmaṇa, an old man, a woman, a child or a cow cannot be killed under any circumstances. Vasudeva stressed that Devakī was not only a woman but a member of Kaṁsa’s family. Because she was now married to Vasudeva, she was para-strī, another man’s wife, and if such a woman were killed, not only would Kaṁsa be implicated in sinful activities, but his reputation as king of the Bhoja dynasty would be damaged. Thus Vasudeva tried in many ways to convince Kaṁsa in order to stop him from killing Devakī.