Ramayana 2.21.41

संश्रुत्य च पितुर्वाक्यं मातुर्वा ब्राह्मणस्य वा।न कर्तव्यं वृथा वीर धर्ममाश्रित्य तिष्ठता।।2.21.41।।

saṃśrutya ca pitur vākyaṃ mātur vā brāhmaṇasya vā | na kartavyaṃ vṛthā vīra dharmam āśritya tiṣṭhatā ||2.21.41||

And having once pledged one’s word—to a father, a mother, or a brāhmaṇa—one who stands taking refuge in dharma, O hero, must not let that promise become vain.