Valmiki Ramayana Sundara Kanda Sarga 51 Shloka 25

तपस्सन्तापलब्ध: obtained by the the virtue of austerity, ते to you, यः that, अयम् this, धर्मपरिग्रहः accumlation of righteousness, आत्मप्राणपरिग्रहः at the cost of your life, सः that, नाशयितुम् to destroy, न न्याय्यः not proper.

"You have acquired the merit of righteousness by prolonged hardships experienced during your penance. It is not proper to forfeit your own life in this way.