During the 1763 Siege of Ft. Pitt Captain Simeon Ecuyer gave representatives of the besieging Delawares two blankets and a handkerchief from the smallpox ward:
Out of our regard to them we gave them two blankets and a handkerchief out of the Small Pox Hospital. I hope it will have the desired effect.
Should there be any ambiguity about "the desired effect":
In a letter to Colonel Henry Bouquet dated July 7, 1763, [Lord Jeffery] Amherst writes "Could it not be contrived to send the Small Pox among those disaffected tribes of Indians?" In a later letter to Bouquet Amherst repeats the idea: "You will do well to try to inoculate the Indians by means of blankets, as well as to try every other method that can serve to extirpate this execrable race."
The Wikipedia article about the Siege of St. Pitt says that these blankets were probably not the actual mechanism by which the Delawares were exposed and infected, but the intention is clear.
The post linked to in the question relates to a different accusation, regarding events in 1837.