According to Official Guinness Records,
The longest marathon playing bass guitar is 41 hr 41 min and was achieved by Mark Edwards (UK) in Westward Ho!, UK, from 30 March to 1 April 2018.Mark attempted this record to raise funds for the Children's Hospice South West. He chose this record as he is a keen endurance athlete and has been playing bass guitar for over thirty years.
For a complete list of 2018 records, please visit 2018 Guinness Records in United Kingdom.