Valmiki Ramayana Yuddha Kanda Sarga 71 Shloka 84

तदा then, आग्नेयेनअस्त्रेण with the missile presided over by fire god, सायकम् arrow, योजयामास concentration of the mind fixed, महात्मनः great self, अस्य his, बाणः arrow, धनुष्य bow.

Then Lakshmana by concentration of his mind fixed on fire god which presided over the arrow, that great selffixed in his bow glowed.