Vādatthika Sutta
Monks, if any ascetic or brahmin should come along seeking an argument with one who has understood as it really is, “This is suffering, this is the cause of suffering, this is the cessation of suffering, this is the way leading to the cessation of suffering,” it is impossible that he could make him shake or tremble.
It is like a stone pillar, sixteen cubits long, with eight cubits sunk into the ground could not be made to shake by the wind.
Therefore, monks, an effort should be made to understand the four noble truths. S.v.445.