Where does the Buddha describe suffering as being like a person who is hit by two arrows?
Probably this: Sallatha Sutta: The Arrow (SN 36.6)

The Blessed One said, &quot;When touched with a feeling of pain, the uninstructed run-of-the-mill person sorrows, grieves, &amp; laments, beats his breast, becomes distraught. So he feels two pains, physical &amp; mental. Just as if they were to shoot a man with an arrow and, right afterward, were to shoot him with another one, so that he would feel the pains of two arrows; in the same way, when touched with a feeling of pain, the uninstructed run-of-the-mill person sorrows, grieves, &amp; laments, beats his breast, becomes distraught. So he feels two pains, physical &amp; mental.
As he is touched by that painful feeling, he is resistant. Any resistance-obsession [etc.]