Warren Buffett left no doubt about the potential he still sees in stocks and his vast skepticism about bitcoin.

During a three-hour, CNBC exclusive interview from Omaha on Monday, the 87-year-old chairman and CEO of Berkshire Hathaway said he would still choose to buy stocks for the long term over bonds, even with the 10-year Treasury yield at around 3 percent.

Buffett said he does not see the stock market in bubble territory. He also calculated a $10,000 investment in an index fund when he bought his first stock in 1942 would be worth $51 million today.

At the same time, Buffett again bashed bitcoin, saying the world's largest cryptocurrency doesn't produce anything except for more buyers looking to make money by selling to new buyers.

Berkshire Vice Chairman Charlie Munger and Microsoft co-founder Bill Gates, also a Berkshire board member, slammed bitcoin as well. They joined Buffett on CNBC's "Squawk Box" on Monday morning. Munger called bitcoin "worthless, artificial gold" while Gates said he would "short it if there was an easy way to do it."