The former president's message after the violence in Charlottesville, Va., was brief, but it hit the right note for many.
"No one is born hating another person because of the color of his skin or his background or his religion ..." Barack Obama tweeted, accompanied by a photo of himself, jacket slung over his shoulder, smiling at four young children gathered at a windowsill.
Twitter has announced that Saturday's tweet is the most-liked tweet ever. It attracted more than 3.3 million likes and 1.3 million retweets as of Wednesday morning.
In the passage quoted by Obama, Mandela writes:
"I never lost hope that this great transformation would occur. Not only because of the great heroes I have already cited, but because of the courage of the ordinary men and women of my country. I always knew that deep down in every human heart, there is mercy and generosity. No one is born hating another person because of the color of his skin, or his background, or his religion. People must learn to hate, and if they can learn to hate, they can be taught to love, for love comes more naturally to the human heart than its opposite. Even in the grimmest times in prison, when my comrades and I were pushed to our limits, I would see a glimmer of humanity in one of the guards, perhaps for just a second, but it was enough to reassure me and keep me going. Man's goodness is a flame that can be hidden but never extinguished."
White House photographer Pete Souza took the photo in the tweet in June 2011.
The caption explains how the moment came to be: "The President had attended the fourth grade closing ceremony for his daughter Sasha at her school in Bethesda, Md. As he was departing, he noticed some pre-school children peering out of a window at a child care facility adjacent to Sasha's school so he walked over to say hello to them."