Dungeons and Dragons – First description or explanation of role play in ODnD?

Does anyone know where the first reference / explanation of role play exists in OD & D (beyond "I are x class")? Dave Arneson is often credited with the advent of what we see today as a role play (addressing NPCs), but he left TSR to publish himself. I have never had a copy of The First Fantasy Campaign to watch.

Heck, where are the first mentions of NPCs as NPCs and not combat statistics? Something more than Sage's description as a Blackmoor resource.