found it for you from a tweet from mod ash - https://twitter.com/...0376832?lang=en
just to support that's all
I can't find any information about this being in OSRS, taken from the OSRS wiki about Slayer Masters:
Each Slayer Master requires a certain Slayer and combat level in order to be assigned monsters.
However, I do think this would be a nice QOL thing to implement regardless.