Udumbarika-Sihanada Sutta

A significant discourse from the Digha Nikaya, this text recounts an encounter between the Buddha and the wanderer Nigrodha at the Udumbarika lodging. The narrative begins with the householder Sandhana seeking the Buddha but finding him in retreat, leading him to visit Nigrodha instead. Nigrodha, surrounded by a noisy assembly, initially disparages the Buddha's wisdom and solitary practice, boasting he could easily defeat him in debate.
The Buddha, overhearing this, approaches the lodging. The discussion then shifts to the merits and demerits of self-mortification, with the Buddha using the metaphor of a tree to illustrate different levels of spiritual attainment, from outer bark to the heartwood of enlightenment. The discourse also touches upon the nature of the Buddha's teaching, emphasizing its transcendence of mere religious rules and its focus on freeing beings from suffering.