“It’s Johnson, always Johnson, who is with me. And if I follow any tradition it is his.” Beckett. Quoted in Frank Doherty, Samuel Beckett
“If by excluding joy we could shut out grief, the scheme would deserve very serious attention, but since however we may debar ourselves from happiness, misery will find its way at many inlets and the assaults of pain will force our regard, though we may withhold it from the invitations of pleasure, we may surely endeavour to raise Life above the middle point of apathy at one time, since it will necessarily sink below it at another.” Johnson, Rambler 47
“I am interested in the shape of ideas, even if I do not believe in them. There is a wonderful sentence in Augustine: I do wish I could remember the Latin. It is even finer in Latin than in English. ‘Do not despair; one of the thieves was saved. Do not presume, one of the thieves was damned.’ That sentence has a wonderful shape.” Beckett. Quoted in Frank Doherty, Samuel Beckett
Time's Flow Stemmed 
Looking around, it appears that the “Augustine” quote may not be from Augustine at all, and most trace it to an Elizabethan named Robert Greene. I shouldn’t mind this so much, except that Beckett says, “It is even finer in Latin than in English.” How awful if he knew it was never written in Latin!
That is curious. Perhaps Beckett heard the phrase from a commentator on Augustine?