How Durva grass became favorite to Sri Ganesha

Once, during a festival in yamapuri, a demon called analasura (the fire demon) was born of Yama. He was as tall as the sky and started terrorizing the worlds. Lord Vishnu, together with Devas and Munis approached Sri Ganesha and sought his help. Sri Ganesha took the form of a small boy and a tough battle ensued between Sri Ganesha and Analasura during which Sri Ganesha swallowed analasura. However, the heat from the stomach started causing much agony to Sri Ganesha. Lord Indra gave Sri Ganesha the moon to wear on his forehead so that he could be cooled off. It was not of much use. Lord Brahma created two kanyas called Siddhi and Buddhi who would help Sri Ganesha to cool off but even this could not take away the heat. Lord Varuna started performing abhisheka with water from all the seas under his control and Lord Siva gave him a thousand headed serpent who tied himself around Sri Ganesha’s tummy to take away the heat. Still the suffering continued. At that time 88,000 sages reached and each one performed archana over Sri Ganesha with 21 Durva grass each. Then only the fire inside could be extinguished. Then Sri Ganesha declared to all those who had assembled that henceforth Durva grass shall be his most favorite puja dravya and even the severest of austerities performed will not make him as happy as being worshipped with durva grass.