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This is a bit off from what you're asking, but results (IMO) are almost always better motivation than a quote. Get an app that tracks your reps and sets. Log every workout that you are able to preform and take your "I can, and I will" attitude and apply it there. Today you can do 10 push ups. Then tomorrow you will do 11. Log your weight if it pleases you. One of the best quotes I ever read was "To appreciate where you are today, you have to see where you were."
As far as a quote app goes: try this
edit: references to my opinions for motivation, not making it a blanket statement.