Oil of Sharpness is a very rare potion in D&D 5e. It does not require attunement.
Potion, very rare
This clear, gelatinous oil sparkles with tiny, ultrathin silver shards. The oil can coat one slashing or piercing weapon or up to 5 pieces of slashing or piercing ammunition. Applying the oil takes 1 minute. For 1 hour, the coated item is magical and has a +3 bonus to attack and damage rolls.