Elon Musk has sold $930 million worth of stock. The richest person in the world and the CEO of Tesla (NASDAQ: TSLA) has sold over 934,000 shares, according to a US Securities and Exchange Commission (SEC) filings on Monday.

The billionaire exercised options to buy 2.1 million stocks at $6.24 each, one of the filings showed.  The CEO of Tesla is obliged to pay income taxes on the difference between the fair market value of the shares and the exercise price. Tesla stock closed at $1,013.39 on Monday.

In fact, this isn’t the first time that Musk exercised his stock options. Before this, the billionaire exercised options to buy acquire about 2.2 million shares, according to a regulatory filing.

This time’s stock sale followed another move by Musk. He sold $6.9 billion worth of shares last week. Additionally, earlier this month, he launched a Twitter poll. On the poll, Musk asked his followers if he should sell 10% of his stock to pay taxes. Some of Musk’s stocks sales today are part of a trading plan established in September, the SEC filings show.

Nonetheless, Musk still owns millions of stock options to exercise before they become expired on August 2022.

The Twitter poll came amid a large debate in the U.S. over whether billionaires are paying enough in taxes. As of this writing, Elon Musk is the richest man in the world. His net worth flirts with the $279 billion mark, according to Bloomberg Billionaires Index.

On Sunday, Musk made fun of Bernie Sanders on Twitter. The senator said that wealthy people should pay their “fair share” of taxes.

"Want me to sell more stock, Bernie? Just say the word," Musk tweeted to Sanders in response. Tesla shares tanked as much as 5% in Monday's session and were down 1% in after-hours trading.