Sandokai is a poem by the eighth Chinese Zen ancestor Sekito Kisen (Shitou Xiqian). It is a fundamental text of the Sōtō school of Zen, and has been chanted in morning services at SokukoJi. Sokuzan teaches from this sutra in today's dharma talk.
https://www.youtube.com/watch?v=TLKY3mUNYRA