Valmiki Ramayana Bala Kanda Sarga 18 Shloka 28

लक्ष्मिसम्पन्न: possessed of auspiciousness, लक्ष्मण: Lakshmana, शरीरत: अपि even by offering his body, सर्वप्रियकर: doing every thing dear to him, तस्य रामस्य for that Rama, अपर: another, बहि: प्राण इव like life moving outside (his body).

Lakshmana, possessed of fortune, was the dearest to his brother than his own body. As though he was his life without.