וְאֶת־כָּל־שְׁלָלָ֗הּ תִּקְבֹּץ֮ אֶל־תּ֣וֹךְ רְחֹבָהּ֒ וְשָׂרַפְתָּ֨ בָאֵ֜שׁ אֶת־הָעִ֤יר וְאֶת־כָּל־שְׁלָלָהּ֙ כָּלִ֔יל לַיהוָ֖ה אֱלֹהֶ֑יךָ וְהָיְתָה֙ תֵּ֣ל עוֹלָ֔ם לֹ֥א תִבָּנֶ֖ה עֽוֹד׃
Mesilat Yesharim
They further said: "'And he shall give you mercy, and have mercy upon you' (Devarim 13:17) - anyone who is merciful to others, will be shown mercy by Heaven" (Shabbat 151b).