Tesla (TSLA) will once again allow customers to pay in bitcoin (BTC-USD) once there's confirmation of "reasonable (~50%) clean energy usage by miners with positive future trend," CEO Elon Musk said via Twitter.Bitcoin rises 8.7% over the last 24 hours to ~$39.1K; the world's biggest cryptocurrency by market cap hasn't breached $40K since May 27.In May, the electric-vehicle maker suspended vehicle purchases using bitcoin due to concern over bitcoin miners' use of fossil fuels, especially coal.Musk was responding to a report in which Sygnia CEO Magda Wierzycka alleged the Tesla founder with manipulating the bitcoin market then selling a "big part of his exposure at the peak."In response, Musk said Tesla only sold ~10% of its holdings "to confirm BTC could be liquidated easily without moving market."Other cryptos also rise. Ethereum (ETH-USD) +4.7% to $2,518, Binance Coin (BNB-USD) +5.4% to $364.68, Cardano (ADA-USD) +6.4% to $1.57, and dogecoin (DOGE-USD) +4.5% to 33 cents.