be inconstant

References in classic literature ?
An individual who is observed to be inconstant to his plans, or perhaps to carry on his affairs without any plan at all, is marked at once, by all prudent people, as a speedy victim to his own unsteadiness and folly.
Yates; and though he and Maria are very good friends, I think she likes Sotherton too well to be inconstant."
"There, behold it there in that lovely figure, in that face, that shape, those eyes, that mind which shines through these eyes; can the man who shall be in possession of these be inconstant? Impossible!
I will not allow it to be more man's nature than woman's to be inconstant and forget those they do love, or have loved.
In spite of Hamlet's desire to ground himself in memory, memory is proven in Hamlet to be inconstant and unreliable.