What did Nanahuatzin and Tecuciztecatl agree to do?

Nanahuatzin and Tecuciztecatl were gods who were both given the chance to become the next sun. Nanahuatzin was a humble god and Tecuciztecatl was a rich and powerful god, but to be the next sun, both had to throw themselves into a huge fire. Tec wanted to do it and stepped forward first but hesitated four times because he feared the fire.