Revelation 6:9-10

And when he opened the fifth sea, I saw, under the altar, the souls of those who were slaughtered on account of the word of God, and the testimony which they held.

Revelation 16:6

for they have poured forth the blood of saints, and prophets; and thou hast given them blood to drink-they are worthy.

Treasury of Scripture Knowledge

Summary

When he maketh inquisition for blood, he remembereth them: he forgetteth not the cry of the humble.

Bible References

When

Revelation 6:9
And when he opened the fifth sea, I saw, under the altar, the souls of those who were slaughtered on account of the word of God, and the testimony which they held.
Revelation 16:6
for they have poured forth the blood of saints, and prophets; and thou hast given them blood to drink-they are worthy.