兩國相爭，不斬來使

两国相争，不斩来使
liǎngguóxiāngzhēng,bùzhǎnláishǐ
when two kingdoms are at war, they don't execute envoys (idiom)

CEDICT

Entry Composition

1 兩國 liǎngguó both countries; the two countries
2 相爭 xiāngzhēng
  1. to vie against one another
  2. to fight each other
  3. mutual aggression
3 不 bù
  1. no; not so
  2. (bound form) not; un-
4 斬 zhǎn
  1. to behead (as form of capital punishment)
  2. to chop
5 來使 láishǐ
  1. (archaic) messenger; envoy
  2. messenger; envoy