Sage agasthiar about birth of neem tree

 While devas and asuras  tried to find amutham the eternal juice which eliminate death lord vishnu beheaded swarna banu an asura who drank amutha which was given only to devas. He became rahu kethu and he cannot drink the juice as his head and body was cut into two. The juice drops he tried to swallow came back from his mouth and due to his nature it became so opposite to sweetness. It took birth in earth as neem tree and is capable of extending ones life.

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