Tesla CEO Elon Musk posted Sunday on Twitter that Tesla will resume bitcoin transactions but only "when there's confirmation of ... 50% clean energy usage by miners."

The comments helped lift the price of bitcoin, which has seen an overall decline since May.

Tesla, the world's largest electric automaker, revealed in an SEC filing in February that it purchased $1.5 billion worth of bitcoin, giving the cryptocurrency a big boost in credibility. But that credibility took a hit in mid-May, when Tesla said it would halt payments with bitcoin due to concerns of how much computer power is needed for mining and how that contributes to climate change.

“We are concerned about rapidly increasing use of fossil fuels for Bitcoin mining and transactions, especially coal, which has the worst emissions of any fuel,” Musk said in May.

Musk has 57 million Twitter followers and has often discussed cryptocurrency, raising concerns about his influence.

His recent tweet was in response to comments from Magda Wierzycka, the billionaire CEO of financial services company Sygnia, who described Musk’s bitcoin tweets as “market manipulation.”

Musk disputed the allegations in his tweet. "Tesla only sold ~10% of holdings to confirm BTC could be liquidated easily without moving market," he posted.

As of Sunday at 5:38 p.m. ET, the price of bitcoin rose 9.04% to $39,073.97. After a recent selloff, bitcoin is still well below its peak in April of about $65,000.