The statistic comes from the World Payments Report 2019 from Capgemini, published on September 17th, 2019.
The report uses Payments Open Banking Assessment which illustrates the state of Open Banking from a payments perspective in 18 markets worldwide. According to the report, "Although cash payments' share of total payment volumes is declining in most countries, cash in circulation (CIC) remained stable or increased slightly over the past five years. Over 30% of countries record higher CIC rates" (WPR 2019, p. 31).
Excerpt World Payments Report 2019
"Interestingly, countries with the highest non-cash transactions volume also continue to be highly dependent on cash.