Reference request: Can a king rule justly without killing? I recall reading a sutta in which the Buddha rises from meditation and says that while he was meditating, it occurred to him: Is it possible for a king to rule righteously without killing? If anyone knows the text I am talking about, it would be much appreciated.
What you are referring to comes from the Discourses of the Sutta Pitaka, and can be found within the book The Connected Discourses of The Buddha; A New Translation of the Samyutta Nikaya by Bhikku Bodhi, Vol. 1, pg 209.

"On one occasion the Blessed One was dwelling among the Kosalans in a small forest hut in the Himalayan region.  Then when the Blessed One was alone in seclusion, a reflection arose in his mind thus: 'Is it possible to exercise rulership righteously: without killing and without instigating others to kill, without confiscating and without instigating others to confiscate, without sorrowing and without causing sorrow?' "

--SN 4.20