This quotation comes from Chapter 24 (Fu/Return--The Turning Point) of the I Ching, or Book of Changes--an ancient Chinese text that combines divination and philosophy. "Chapter 24" is also known to many music fans as a track from the 1967 Pink Floyd album The Piper at the Gates of Dawn. The song opens with the lines quoted by Anzaldúa.
Read all 64 of the I Ching messages on the Deoxyribonucleic Hyperdimension website. The messages are based on a system of trigrams (made up of short and long lines) that is often depicted in the form of the Pakua, centered by the Taoist "yin yang" symbol depicting the unity of opposites.