The Parable of the Mandarin Duck and Kacalindikaka

“Also, next, oh good man! The Buddhist teaching is like the mandarin duck [and kacalindikaka] who always go together (although they are different birds). The mandarin duck and the kacalindikaka seek the highlands at the summer solstice, when the water level is high, and deposit their young there. This is to induce their growth. Later, they will act as they originally ought to. The same happens with the appearance of the Tathagata. He teaches innumerable beings and enables them to abide in the Wonderful Dharma. This is like the mandarin duck and the kacalindikaka seeking highlands and putting their young safely there. The same goes with the Tathagata. He enables beings to act as they ought to act and (later) enables them to enter Mahaparinirvana. Oh good man! This means that suffering is a teaching [dharma] and bliss is a different [dharma]. All created things are grief, Nirvana is Bliss. It is (Nirvana) the most wonderful and destroys created things [i.e., lifts us beyond the created sphere]."

Read More on the Nirvana Sutra, Chapter 14 - On the Parable of the Birds.