Bitcoin escalated over $39,000 after Elon Musk said that Tesla Inc. may restart transactions with the digital currency when mining is carried out with more clean energy.

Tesla’s CEO, Musk said that the e-car manufacturer will allow Bitcoin transactions again upon confirmation of reasonable (~50%) clean energy usage by miners with a positive future trend.

His tweet was a reply to a report in Cointelegraph. The report mentioned executive chair of South African asset manager Sygnia Magda Wierzycka, as saying Elon’s current posts on Bitcoin should’ve evoked an investigation by the U.S. Securities and Exchange Commission.

In New York, on Sunday afternoon the crypto jumped as much as 9.3% to $39,372, the highest level since June 3 and just below the $40,000 level seen as key by some chart watchers. In Hong Kong on Monday as of 7 a.m., it was down about 1%.

In the past few months Musk has whipsawed other digital tokens and Bitcoin. Tesla made it official that it had purchased $1.5 billion in Bitcoin and indicated its intent to begin accepting Bitcoin as payment for vehicles, in February. Musk tweeted in March that you can now purchase a Tesla with the Bitcoin. But again in May, he stated that the practice was halted because of concerns about fossil-fuel usage for Bitcoin transactions and mining.