AV 1.23

And thou shalt have great sickness by disease of thy bowels, until thy bowels fall out by reason of the sickness day by day.

In their hearts is a disease, and Allah increaseth their disease. A painful doom is theirs because they lie.

But Hector, from this scene of slaughter far, Raged on the left, and ruled the tide of war: Loud groans proclaim his progress through the plain, And deep Scamander swells with heaps of slain. There Nestor and Idomeneus oppose The warrior’s fury; there the battle glows; There fierce on foot, or from the chariot’s height, His sword deforms the beauteous ranks of fight. The spouse of Helen, dealing darts around, Had pierced Machaon with a distant wound: In his right shoulder the broad shaft appear’d, And trembling Greece for her physician fear’d. To Nestor then Idomeneus begun: “Glory of Greece, old Neleus’ valiant son! Ascend thy chariot, haste with speed away, And great Machaon to the ships convey; A wise physician skill’d our wounds to heal, Is more than armies to the public weal.” Old Nestor mounts the seat; beside him rode The wounded offspring of the healing god. He lends the lash; the steeds with sounding feet Shake the dry field, and thunder toward the fleet.

It is simply by being pained at (the thought of) having this disease that we are preserved from it. The sage has not the disease. He knows the pain that would be inseparable from it, and therefore he does not have it.