Where do you get the whetstone recipe in Minecraft (when do you unlock it)?

Where do you get the whetstone recipe in Minecraft (when do you unlock it)?

By having one of the required materielian in your inventory. Here is the recipe: https://minecraft.fandom.com/de/wiki/Schleifstein

If you have the materials for it in your inventory it should be displayed.

if not (i.e. If it doesn't appear like this) you can just do it like this