Joshua 20:3

that the manslayer who in innocence strikes anyone mortally, without knowing, may flee there. And they shall be your refuge from the avenger of blood.

Treasury of Scripture Knowledge

Summary

That the slayer that killeth any person unawares and unwittingly may flee thither: and they shall be your refuge from the avenger of blood.

General references

Bible References

General references

Numbers 35:19
The revenger of blood himself shall kill the murderer. When he meets him, he shall kill him.