A loyal friend is a powerful defense: whoever finds one has indeed found a treasure.

The Bible (The Old Testament) (14th - 2nd C BC) Judeo-Christian sacred scripture [Tanakh, Hebrew Bible], incl. the Apocrypha (Deuterocanonicals)

Sirach (Ecclesiasticus) 6:14 [NJB (1985)]
    (Source)

Alternate translations:

A faithful friend is a strong defence: and he that hath found him, hath found a treasure.
[DRA (1899)]

A faithfull friend is a strong defence: and he that hath found such an one hath found a treasure.
[KJV (1611)]

A loyal friend is like a safe shelter; find one, and you have found a treasure.
[GNT (1976)]