Sword of Wounding
Weapon (any sword), rare, requires attunement · 2014 rules, SRD 5.1
HP lost to it regain only on a short or long rest; once per turn a hit wounds: 1d4 necrotic at the start of each of its turns per wound until a DC 15 Con save.
Also in the 2024 rules (SRD 5.2).