A tweet from Warren Buffett is a big deal. In fact, when multi billionaire Warren Buffett tweeted for just the sixth time on Thursday, it was national news.

Buffett, who has over 900,000 Twitter followers even though he hasn’t tweeted in more than 12 months, surprised his followers Thursday with a tweet to promote a new campaign from Facebook CEO Sheryl Sandberg’s LeanIn.org.

Warren Buffett Supports #LeaninTogether With Rare Tweet

Sending the hashtag “#LeanInTogether,” Buffett included a photo of himself with Mary Rhinehart, the CEO of a Berkshire Hathaway manufacturing holding company named Johns Manville, in the tweet. He noted that Rhinehart is “successfully running a $2.5B company in a male-dominated field.”

Warren Buffett is a long-time supporter of women in the workplace

It’s a matter of public record that Buffett has worked to promote equality for women in the workplace for many years. He’s said on several occasions that much of his success is due to his male gender and when and where he was born. He’s also commented in the past that his “floor” in life was his sister’s “ceiling.” Buffett has also noted on several occasions that unlocking the full potential of women is critical to America’s future prosperity.

Buffett’s very first tweet was to promote his participation in Fortune’s Most Powerful Women Summit in 2013.

More on LeanIn

Thursday’s tweet appeared to be part of a larger Twitter campaign focusing om a new initiative by LeanIn.org, a website launched by Facebook CEO Sheryl Sandberg. Her book of the same name highlighted the various ways women are held back professionally, and pointed out that women often hold themselves back.

The #LeanInTogether page of the website that Buffett’s tweet referred to asks men to “show the world you’re in for equality” and provides a number of tips for men “for pushing back against gender bias in the office” and “to support your partner and children” at home and at play.