Bhagavad Gita 1.22

So that I may observe those who must fight on my side and those who must fight against me.

यावदेतान्निरीक्षेऽहं योद्धुकामानवस्थितान्।
कैर्मया सह योद्धव्यमस्मिन्रणसमुद्यमे॥

yāvadetānnirīkṣe'haṃ yoddhukāmānavasthitān|
kairmayā saha yoddhavyamasminraṇasamudyame||

English translation (above): Shri Purohit Swami (1935), public domain. Sanskrit text via github.com/gita/gita (Unlicense).