Valmiki Ramayana 6.79.26

विद्धमन्योन्यगात्रेषु द्विगुणं वर्धते परम्।कृतप्रतिकृतान्योन्यं कुरुतां तौ रणाजिरे॥

viddhamanyonyagātreṣu dviguṇaṃ vardhate param |kṛtapratikṛtānyonyaṃ kurutāṃ tau raṇājire ||

Our plain-language meaning of this verse is waiting for scholar review.