The sale came after Musk on Monday clinched a deal to buy Twitter for $44 billion in cash in a transaction that will shift control of the social media platform populated by millions of users and global leaders to the world's richest person. Musk's net worth is $268 billion, according to Forbes.
As part of the deal, Musk said he would provide a $21 billion equity commitment.
It was not immediately clear how the billionaire would raise the remaining $12.5 billion of equity financing. Musk holds a 43.61 per cent stake in unlisted rocket company SpaceX, which is reportedly valued at $100 billion.
Tesla shares rose about 5 per cent in morning trading on Friday.
They have tumbled about 20 per cent since Musk's disclosure of a more than 9 per cent stake in Twitter on 4 April.
Musk has been looking for partners to reduce his equity contribution to the deal, a person familiar with the matter told Reuters, adding that it is far from certain such a partner will emerge.
This is his first Tesla stock sale since he offloaded $16.4 billion worth of shares in November and December after polling Twitter users about selling 10 per cent of his stake in the electric car maker.
Musk said on Twitter that he would pay more than $11 billion in taxes in 2021 due to his exercise of stock options set to expire this year.
Some traders have fretted this week that Musk may not have enough money sitting around to fund his $21 billion cash contribution and could walk away from the deal, weighing on Twitter shares.
As part of the Twitter financing deal, Musk secured commitments for $13 billion in loans secured against Twitter and a $12.5 billion margin loan tied to his Tesla stock.