You go tell Mason is a holotape in the Fallout 4 add-on Nuka-World. It is recorded by a Pack raider.
Location
The tape can be found in the Nuka-Town backstage, on a table in the room with a chemistry station and animal cages.
Transcript
Raider Man: I told you that cow was trouble. She took off with all the chems. ALL OF THEM! What are we going tell Mason? This is the last time I let your pecker risk mine. You go tell Mason what happened. And you leave my name the fuck out of it. If you're still alive tomorrow maybe we can still be friends.
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