Here are a few of my favorite strength quotes:
"The real man smiles in trouble, gathers strength from distress, and grows brave by reflection."
"The true test of any man lies in action."
"Greatness lies not only in being strong, but in the right use of strength".
— Henry Ward Beecher
"Do not pray for easy lives. Pray to be stronger men!"
— Phillips Brooks
"The man who says it cannot be done should not interrupt the man who is doing it."