The Big Bird and the Island of Gold and Silver

A young boy was told by a big bird to take him to an island of gold and silver. He did as he was told, but could hardly open his eyes because there was so much treasure. The little brother became very rich after taking the grain back to market. His family were jealous and asked where he'd gotten all the gold and silver from. But when they found out it had come from their younger brother's seed - that is what led them to this story.