Valmiki Ramayana Yuddha Kanda Sarga 12 Shloka 28

सलक्ष्मणस्य: accompanied by Lakshmana, रामस्य: Rama's, सीता: Sita, प्रसह्य: by force, यदा: at that time, इह: here, अहृता: brought, तदा: then, सकृत् formerly, समीक्ष्यैव: should have discussed, चित्तम् mind, यमुना: Yamuna, यामुनमिव: like it fills Yamuna mountain, सुनिश्चितम् decided, भजेत: would be.

"If you had at that time, that is before bringing Sita by force, which was accompanied by Rama and Lakshmana, discussed, and thought of, then you would be sure in your mind like the Yamuna River filling the Yamuna (mountain )."