2 Chronicles 20:12
אֱלֹקינוּ הֲלֹא תִשְׁפָּט בָּם כִּי אֵין בָּנוּ כֹּחַ לִפְנֵי הֶהָמוֹן הָרָב הַזֶּה הַבָּא עָלֵינוּ וַאֲנַחְנוּ לֹא נֵדַע מַה נַּעֲשֶׂה כִּי עָלֶיךָ עֵינֵינוּ
Our G-d, will You not execute judgment on them? For we have no strength against this great multitude that comes against us, nor do we know what to do, so our eyes are upon You.
This verse, quoting the words of King Yehoshafat, is cited in Tachanun. Eicha Rabbosi contrasts the ways of four kings. David pursued his enemies and destroyed them; Asa pursued but did not have the strength to destoy; Yehoshafat did not even have the strength to pursue, so he prayed; Chizkiyahu did not even possess that much strength. The Midrash’s understanding of Yehoshafat’s approach is based on this verse.