unquestionable sources

"[Mable Ong] had a positive manner of speaking, now and then turning her head aside to cough or laugh; she spoke bitterly about capitalism and would relate stories she had heard from unquestionable sources about women dying in childbirth because they could not afford the high cost of hospitalization, or even the cost of insurance programs."

~~ from  Mrs. Bridge  by Evan S. Connell