At the end of Sui Dynasty, a traitor was at odds with Li Yuan. Therefore, he voted for Yang Di and proposed that Tang Yuan build a grand palace for the emperor within 100 days, and if it could not be repaired by then, Tang Yuan would be executed. Therefore, Li Yuanhua paid a lot of money to invite many skilled craftsmen to build the palace in less than 100 days.
But the traitor said that Tang Gaozu had repaired the palace. Yang Di also called Tang gaozu to the imperial court and pushed him out to be beheaded. Just then, your highness heard a loud cry: "your majesty, you have been wronged!" Please leave people under the sword. "
It turned out to be Li Shimin, the second son of Tang gaozu. He knelt down and bowed down, reported his name and life, and said, "My father has been wronged! This palace was really built in a hundred days. Please send someone to pull out nails for rust inspection, uncover tiles and check mud. In the newly-built palace, the nails are not rusted, and the tile mud is still new. If it had been repaired earlier, the nails would have rusted and mildew spots would have appeared on the tiles. " Yang Di immediately sent someone to check, and it turned out that the palace was newly built. So he rewarded Li Yuan and his son and punished the traitor who slandered them.