What is the authenticity of Herodotus's explanation on mummification?where did he get the soucres from for it?

Answer 1

From the Egypt State Information Service:

Herodotus got his information from wandering about the country and asking questions and making observations. And the Information Service notes that his information was gathered in the 5th century BC, and as such was "relatively late in date."

Answer 2

Supposedly he interviewed people in Egypt who actually performed mummifications. The only problem is that the people he interviewed were not as adept at mummification as were the people of more ancient times in Egypt.