A Song of Ascents. Of David.

133:1   Behold, how good and pleasant it is
    when brothers dwell in unity!
2   It is like the precious oil on the head,
    running down on the beard,
  on the beard of Aaron,
    running down on the collar of his robes!
3   It is like the dew of Hermon,
    which falls on the mountains of Zion!
  For there the LORD has commanded the blessing,
    life forevermore.

(ESV)