Last week, he said in documents filed with US securities regulators that the money would come from Morgan Stanley and other banks, some of it secured by his huge stake in the electric car maker.
Twitter has not commented.
Musk has said he wants to buy Twitter because he doesn't feel it's living up to its potential as a platform for free speech.
In recent weeks, he has voiced a number of proposed changes for the company, from relaxing its content restrictions — such as the rules that suspended former President Donald Trump's account — to ridding the platform of its problems with fake and automated accounts.
Musk is the world's wealthiest person, according to Forbes, with a nearly US$279b fortune. But much of his money is tied up in Tesla stock — he owns about 17 per cent of the company, according to FactSet, which is valued at more than US$1 trillion — and SpaceX, his privately held space company. It's unclear how much cash Musk has.