I always thought that this was a quote from Abraham Lincoln, but Jon Meacham, in his book And There Was Light–Abraham Lincoln and the American Struggle, attributes it to Theodore Parker.
I hope we are bending toward justice.
“I do not pretend to understand the moral universe: the arc is a long one, my eye reaches but little ways. I cannot calculate the curve and complete the figure by experience of sight. I can divine it by conscience. And from what I see I am sure it bends toward justice,” Theodore Parker once said.