A saint is a sinner who keeps trying.–attr. St. Josemaría Escrivá
This saying is also attributed to St. Teresa of Calcutta and to Nelson Mandela. The closest form of it I can find in St. Josemaría’s work is this:
Don’t forget that the saint is not the person who never falls, but rather the one who never fails to get up again, humbly and with a holy stubbornness.–In the Footsteps of Christ, 131.
Without disrespect to St. Josemaría, I will say that I strongly doubt that the idea is original to him, and I doubt even more that he’s responsible for the original quotation.
As for Nelson Mandela, the closest I can find is this:
No axe is sharp enough to cut the soul of a sinner who keeps on trying, one armed with the hope that he will rise even in the end.–Letter to Winnie Mandela (1 February 1975)
I can’t find a reliable source attributing it to Mother Teresa at all.
ETA: A friend tells me that it’s also attributed to Robert Louis Stevenson. Wikipedia tells me that RLS was a self-professed atheist, and a Google Books search through his works turns up nothing.
They didn't say it 