The gemora in Bava Metzia in Perek Hazahav describes the power of Tachnun where Rebbi Eilezer was the brother in law of Rabon Gamliel. The wife of Rebbi Eliezer did not allow him to fall on his face in order not to hurt her brother. One day she miscalculated and she told him get up you just killed my brother. Be careful if you have taanus against someone, one did something bad to you, not to hurt them through tachnun.
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