This sent Panasonic's stock soaring about 6% in trading in Japan on Wednesday. The stock ended the day up 3.7%.
"Would like to clarify that Tesla is working exclusively with Panasonic for Model 3 cells," Musk wrote on Twitter. "S and X cells are also Panasonic."
On Tuesday, Reuters had reported that a source familiar with the matter said the manufacturer of electric cars was in talks with Samsung SDI to begin supplying electric batteries for Tesla's mass-market electric car the Model 3.
Panasonic last month said it would bring forward its investment in Tesla's battery plant. The company plans to contribute $1.6 billion to Tesla's $5 billon "Gigafactory" to meet the demand for the Model 3.
Tesla was up slightly in pre-market trading on Wednesday. The shares on Tuesday closed up 5.3% to end the day at $232.34.
The shares surged in mid-afternoon on Tuesday after investor Ron Baron told CNBC that Tesla could be one of the largest companies in the world. The CEO of Baron Capital said that he could see holding the stock for the next 10 to 20 years and that the investment could generate between $6 billion and $7 billion.