Facebook founder and CEO Mark Zuckerberg was the principal speaker at Harvard University's 366th Commencement Day on Thursday, and as he closed his speech, he shared the Jewish prayer he sings over his daughter every night.

"Before you walk out those gates one last time, as we sit in front of Memorial Church, I am reminded of a prayer, Mi Shebeirach," he told Harvard's Class of 2017.

Zuckerberg said he sings the prayer to his daughter each night when he tucks her in. He also recites it whenever he faced challenges.

The prayer goes: "May the source of strength, who blessed the ones before us, help us find the courage to make our lives a blessing."

'Mi Shebeirach' is traditionally spoken as a blessing. It can be spoken over an individual or a group needing divine favor. Most people declare it for those who need healing. 'Mi Shebeirach' gets its name from the first line: "May He who blesses ... "

The prayer is quite flexible, and the words can be adjusted depending on the kind of blessing a person or group needs, or how the person declaring the blessing wants them to be blessed.

The lines that Zuckerberg sings to his little girl at night come from one of the most popular versions of the prayer sung by Jewish musician Debbie Friedman, who was known to transform the teachings of Judaism into beautiful songs that people can easily relate to.

The English lines of the song say "May the source of strength, who blessed the ones before us, help us find the courage to make our lives a blessing ... Bless those in need of healing with full recovery, the renewal of body, the renewal of spirit. And let us say Amen."

Zuckerberg, who grew up in New York, was raised Jewish, but somewhere along the way, he began identifying as an atheist. On December last year, he surprised everyone by posting a "Merry Christmas and Happy Hanukkah" greeting on Facebook.

The post led someone to ask if he was an atheist, as many people believed him to be. Zuckerberg confirmed he did identify as an atheist, but at this point in his life, he realized the importance of religion.

"I was raised Jewish and then I went through a period where I questioned things, but now I believe religion is very important," he replied to the person who asked about his former atheism.

At Harvards's commence address, Zuckerberg encouraged the graduates to "do great things."

"Let me tell you a secret: no one does when they begin. Ideas don't come out fully formed. They only become clear as you work on them. You just have to get started," he said. "If I had to understand everything about connecting people before I began, I never would have started Facebook."

He shattered the idea of "a single eureka moment" often witnessed in movies, saying it makes people feel inadequate and "prevents them from getting started."

"It's good to be idealistic. But be prepared to be misunderstood. Anyone working on a big vision will get called crazy, even if you end up right," he said.

Zuckerberg closed his speech with a powerful line of encouragement.

"I hope you find the courage to make your life a blessing," he said.