Those who are cruel to the kind, are kind to the cruel. I heard it was stated in the Talmud, but not able to find it. Thoughts?
Midrash Tanchuma Parashat Metsora
R. Eleazar said, “Anyone who becomes merciful upon the cruel one will end by being cruel to the merciful: It is written (I Samuel 15:9), ‘But Saul had pity upon Agag and upon the best of the sheep and the cattle’; and it is [also] written (I Samuel 22:19) about Nob the city of priest, ‘And he smote Nob the city of priests with the edge of the sword.’
Pretty much identical to the above but said elsewhere by someone else....
רַבִּי שִׁמְעוֹן בֶּן לָקִישׁ אוֹמֵר, כָּל מִי שֶׁנַּעֲשָׂה רַחְמָן בֵּמְקוֹם אַכְזָרִי, סוֹף שֶׁנַּעֲשָׂה אַכְזָרִי בִּמְקוֹם רַחֲמָן, וּמִנַּיִן שֶׁנַּעֲשָׂה אַכְזָרִי בִּמְקוֹם רַחְמָן, שֶׁנֶּאֱמַר (שמואל א כב, יט): וְאֶת נֹב עִיר הַכֹּהֲנִים הִכָּה לְפִי חֶרֶב, וְלֹא תְהֵא נֹב כְּזַרְעוֹ שֶׁל עֲמָלֵק
Rabbi Shimon ben Lakish said - All those who are merciful in a place of cruelty, in the end they are being cruel in a place of mercy. And from where do we know that one makes themselves cruel in a place of mercy - as it says (Shmuel I 22:19) "And Nov, the city of Kohanim , he smote by the sword" and Nov shall not be like the seed of Amalek.