news source; source of information
Used in journalism and reporting contexts for the person, document, or entity that provides information for a news article or report.
The reporter did not reveal the source of the information.
We obtained the information from a reliable source.
ニュースソース is a direct loanword equivalent, often used in casual or media contexts, but 取材源 is more formal and specifically tied to the act of news coverage (取材).
Compound of 取材 (news gathering, reporting) and 源 (source, origin).