From “Conversation of birds”:
King of birds Simurg drops a magnificent feather; the birds which are tired of discord decide to find it. They know that the name of the king means “Thirty birds”, that his palace is situated on Kafa, a mountain or a mountain ring-shaped ridge which circumvents the earth. At first some birds demonstrate cowardice: nightingale refers to his love to rose; parrot — to his beauty for the sake of which he has to live in a birdcage; partridge cannot part from its hills, heron — from swamps and owl — from ruins. Finally they undertake this daring journey; they overcome seven valleys and seas. Many pilgrims quit, others perish during the passage. And thirty birds who have reached purgation owing to their work alight on Simurg mountain. Finally they saw it, and here they understand that they themselves are “Simurg”, and that “Simurg” is each of them and all of them together.
According to the ancient legend Simurg is an immortal bird who has its nest in the branches of the Tree of Knowledge.