Here are some quotes about inner strength:
"Mistakes are always forgivable, if one has the courage to admit them." - Bruce Lee
"Nothing can dim the light which shines from within." - Maya Angelou
"The greatest glory in living lies not in never falling, but in rising every time we fall." - Nelson Mandela
"You have power over your mind―not outside events. Realize this, and you will find strength." - Marcus Aurelius
"No matter what kind of challenges or difficulties or painful situations you go through in your life, we all have something deep within us that we can reach down and find the inner strength to get through them." - Alana Stewart
"I was always looking outside myself for strength and confidence but it comes from within. It is there all the time." - Anna Freud
"We acquire the strength we have overcome." - Ralph Waldo Emerson
"Most of the important things in the world have been accomplished by people who have kept on trying when there seemed to be no hope at all." - Dale Carnegie
"Strength and growth come only through continuous effort and struggle." - Napoleon Hill
"Strength does not come from physical capacity. It comes from an indomitable will." - Mahatma Gandhi
"It is not because things are difficult that we do not dare; it is because we do not dare that they are difficult."
I hope you find these quotes helpful.