What is the name of this Aztec legend?

Sometimes it is referred to as the myth of creation. Sometimes it is just a side story as to how Tezcatlipoca lost his foot and replaced it with an obsidian mirror. "In the Creation story Tezcatlipoca and his brother Quetzalcoatl were sent to earth fo fight Cipactli, the crocodile like Earth Monster who lived under the water. Tezcatlipoca stuck his foot into the water trying to lure the monster out, and as he did so Cipactli bit his foot off. The other tells how he feel in love with Xochiquetzal, the moon and flower goddess and wife of Tlaloc the rain god. When he tried to seduce the goddess her enraged husband threw him off their heavenly mountaintop and he lost his foot. He replaced it with an obsidian mirror."