Valmiki Ramayana Bala Kanda Sarga 56 Shloka 5
Original Shlokaतस्यास्त्रं गाधिपुत्रस्य घोरमाग्नेयमुद्यतम्। ब्रह्मदण्डेन तच्छान्तमग्नेर्वेग इवाम्भसा।।1.56.5।।
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तस्य गाधिपुत्रस्य that Gadhi's son's, उद्यतम् discharged, तत् that, आग्नेयम् Agneya, अस्त्रम् weapon, अम्भसा by water, अग्ने: fire's, वेग: इव like speed, ब्रह्मदण्डेन by the rod of Brahma, शान्तम् calmed.
The Brahmadanda (released by Vasishta) put down the dreadful agneya astra released by Gadhi's son just like the force of fire is extinguished by water.