"proof of strength" is a correct and commonly used phrase in written English.
It is typically used to refer to evidence or demonstration of one's physical or mental prowess or fortitude. Example: "The weightlifter's ability to lift 500 pounds was a clear proof of his strength." Other examples: 1. "The marathon runner's record-breaking time was a testament to her proof of strength." 2. "Facing all the challenges in his life with determination was a proof of his inner strength." 3. "Winning the chess tournament against tough opponents was a solid proof of the player's mental strength."
The first proof of its strength came in a 2003 primary victory over a Syracuse councilman who had broken a promise to support a living-wage ordinance.
The gesture was not only irresistible metaphor — he didn't want the flame to die — but also showy proof of his strength.
Ryan Jones led Wales in 2008 but has spent much of this year on the bench, proof of the strength in depth Wales have built up in the last year that allows them to replace players seamlessly.
But there is, I think, something new in the most modern of these open-air movements - Kibbo Kift Kindred, whose queer-sounding name comes from an old Cheshire expression meaning "strong" or "proof" of great strength.
When Tuilagi then brushed aside Carter and McCaw to set up Chris Ashton for his first Test try in 14 months, it was further proof of the strength of character Lancaster and his coaches have worked so hard to instil.
But the lack of Qaeda violence on the May 2 anniversary has been taken by some analysts as further proof of waning strength — as has the recent scarcity of the once-plentiful videos issued by Mr. Zawahri.
In terms of competition films, Dargis was impressed by Jacques Audiard's "sweeping and precisely observed" A Prophet, the "extraordinary tactility" of Jane Campion's Bright Star and Corneliu Porumboiu's Police, Adjective, "further proof of the strength of the Romanian New Wave".
Proof of the strength of the Smiths B-sides was that this, perhaps their defining statement, crept out on the flip of the 12" single of William, It Was Really Nothing, alongside the almost equally loved Please, Please, Please Let Me Get What I Want, though that was apparently because Rough Trade boss Geoff Travis didn't fancy it as an A-side.
Project Unbreakable is proof of the strength of survivors.
