Slander and Avici Hell?
For bikkhus, You can look at the vinaya, Monks’ Pācittiya 3,
https://suttacentral.net/pli-tv-pvr1.2/en/horner-brahmali

the buddha says that you go to hell when you slander the buddha or the noble ones, like here https://suttacentral.net/sn6.9/en/sujato

https://suttacentral.net/t211.30/en/beal

but for slander of a puthujjana by another puthujjana, that's seems to be the usual harsh speech, so no explicit direct destination.