Ramayana
बहवः पार्थिवा राजन्नतिक्रान्ता महाबलाः । कार्यस्य गौरवं मत्वा प्रतिज्ञां नाभ्यरोचयन् ॥ 7-60-17 ॥
"Many mighty kings before you, O king, have passed away, for, weighing the gravity of the task, they did not consent to such a vow."
english translation