Musar על ערכין 29:11

From this portion we can learn how great is the penalty for indulging in evil gossip. By doing so, a person causes harm to himself as well as to the world at large. The spies caused harm to the whole nation of Israel, but the greatest harm they caused themselves. Our sages in Pesikta Zutra Metzora, comment that if people who only spread lies about stones and and trees were subjected to such punishments, how much more serious is it to spread lies about human beings, about one's fellow man!