REV 6:9

9 And when he opened the chotam hachamishi [(fifth seal)], I saw underneath the Mizbe'ach [(altar)] the nefashot [(souls)] of the ones having died al kiddush ha-Shem, having been slain as martyrs because of the dvar Hashem[(word of G-d)] and because of their solemn eidus [(testimony)] which they had given.