Ramayana
यदि ह्यन्मिन्निपतिते न म्रियेतैष राक्षसः । म्रियते वा दशग्रीवस्तदाप्युभयतो ऽनृतम् ॥ 7-22-45 ॥
"For if, when it has fallen upon him, this Rakshasa should not die, or if Ravana the Ten-necked should die, then in either case there is falsehood."
english translation