Matthew 23:27

Woe to you, you irreligious scribes and Pharisees! you are like tombs white-washed; they look comely on the outside, but inside they are full of dead men's bones and all manner of impurity.

Luke 11:44

Woe to you! you are like unsuspected tombs; men walk over them unawares."

Treasury of Scripture Knowledge

Summary

And whosoever toucheth one that is slain with a sword in the open fields, or a dead body, or a bone of a man, or a grave, shall be unclean seven days.

Bible References

A grave

Matthew 23:27
Woe to you, you irreligious scribes and Pharisees! you are like tombs white-washed; they look comely on the outside, but inside they are full of dead men's bones and all manner of impurity.
Luke 11:44
Woe to you! you are like unsuspected tombs; men walk over them unawares."