There is no sin for a king who kills for the right cause, who is engaged in maintaining his citizens. But this injunction is not applicable to me.
Srimad Bhagavata Purana
श्रीमद्भागवतमहापुराणम्
मूल श्लोकः
नैनो राज्ञः प्रजाभर्तुर्धर्मयुद्धे वधो द्विषाम् । इति मे न तु बोधाय कल्पते शासनं वचः
naino rājñaḥ prajābharturdharmayuddhe vadho dviṣām | iti me na tu bodhāya kalpate śāsanaṃ vacaḥ
SB 1.8.50