Could be spelled firsthand, one word, or first-hand.

"Firsthand knowledge" is knowledge gained through direct experience or observation.

Firsthand - 2003 was released on:

USA: 1 July 2003

they are a firsthand account by a slave

Firsthand data is information that is collected directly from the source or through direct experience. This type of data is considered more reliable and accurate as it is obtained firsthand rather than being interpreted or communicated by others. Examples of firsthand data include observations, surveys, interviews, and experiments.