When he opened the fifth seal,
I saw underneath the altar the souls of those who had been killed for the Word of God, and for the testimony of the Lamb which they held.
They cried with a loud voice, saying, “How long, O Lord, holy and true,
until you judge and avenge our blood on those who dwell on the earth?”
A long white robe was given to each of them.
They were told that they should rest yet for a while,
until their fellow servants and their brothers,
who would also be killed even as they were,
should complete their course. Revelation 6:9-11

After the opening of the fifth seal
the righteous will be asking;

How Long O Lord?