[If he says:] “I am a nazir [as much] as the hair on my head,” or “the dust of the earth,” or “the sand of the sea” —- he is a nazir forever, and he shaves [his head] once every thirty days. Rabbi says: This one does not shave [his head] once every thirty days. Who is the one that shaves [his head] once every thirty days? One who says: “Let there be [an obligation] of nezirus upon me [as much] as the hair of my head,” or “as the dust of the earth,” or “as the sand of the sea.’’