This is what I have heard. “Monks, the lion is the king of beasts. In the evening he comes out of his lair. And when he comes out, he stretches himself. Then he surveys the four quarters in full and roars his lion’s roar, three times. Then, once he has roared his lion’s roar, he sets off in search of food. What is the reason for this? He thinks: “Let me not bring about the death of small creatures that have wandered astray.” And ‘lion,’ monks, is a term for the Tathagata, an arahat who is a perfectly awakened buddha. And when the Tathagata teaches in an assembly, that is his lion’s roar.”

From Sayings of the Buddha: A Selection of Suttas from the Pali Nikayas, translated by Rupert Gethin, Oxford: Oxford University Press, 2008, p. 266.