Sasswood

This man, being informed of his sentence, pleaded innocence, and said he himself would drink Sasswood water to prove it. His friends urged him to confess, as his brother, the king, said he had no ill will against him, and did not wish him to drink the Sasswood, unless it was his own pleasure to do so. He still, however, persisted in his wish to make the trial. Four pieces of the Sasswood tree, each about the size of a finger nail, were then prepared for him; […]

Source: wiktionary

[…] He wondered what sasswood was—Delah had sworn by sasswood that she was telling the truth when the coaxed those in the shadow village out of hiding. Delah explained that many years ago, before the Americos starting intefering in tribal business, trial by sasswood was a way of determining whether a person accused of a crime was innocent or guilty. The bark of a particular tree was mashed to make a "truth serum." If the accused died after drinking the concoction, he was guilty. Refusal to drink was also an indication of guilt, in which case the accused was executed.

Source: wiktionary