TANAKH
And the Lord said to Moshe, Speak to the priests the sons of Aharon, and say to them, There shall none be defiled for the dead among his people:
MIDRASH
Rabbi Shmuel bar Nahmani said:
They said to it: ‘Why do you bite one limb but your venom disseminates to all the limbs?’
It said to them: ‘Do you say this to me: “There is no advantage to the master of the tongue”?’ (Ecclesiastes 10:11). One sits in Rome and kills in Syria, in Syria, and kills in Rome.
Why is it called "third"?
It is because it kills three: The one who spoke it, the one who accepts it, and the one about whom it is spoken.
There was an incident involving a man who had an evil daughter-in-law who constantly spoke slander. He would plead with her twice a day, once in the evening and once in the morning.
He would say to her: ‘I implore you not to speak slander.’
What did she do? She went and told her husband: ‘This father of yours sought to have relations with me. If you do not believe me, come this evening and you will hear him sitting and pleading with me.’
He went and lay in wait for him and saw him standing bowed and speaking to her.
He said: ‘The matter has proven true.’
What did he do? He struck his father and killed him.
They took him to trial and he was sentenced to death. That woman who spoke slander about his father was also sentenced to death. It was thus found that the tongue killed the three of them.
PERSONALITIES
Shmuel bar Nahmani -
A amora, who lived in the Land of Israel from the beginning of the 3rd century until the beginning of the 4th century
INSIGHTS
Called "third": See Tractate Arachin 15b.