Joshua 20:3

so that the manslayer who kills any person in error and without knowledge 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 kinsman avenger of blood shall slay the murderer; when he meets him, he shall slay him.