Merlin's beard

Merlins Beard is a common wizarding term used in shock such as its first appearance, with "Merlins beard, you must be harry potter!", Ron Weasley also frequently uses merlin in other expressions such as "what in the name of merlins pants is that?".

The orgions of the expression is unknown, it does however tend to be used when muggles would use gods name in vain such as "My God!".