Valmiki Ramayana Ayodhya Kanda Sarga 21 Shloka 41

वीर O hero, पितुः of father, मातुर्वा or of mother, ब्राह्मणस्य वा or of brahmins, संश्रुत्य having promised, धर्मम् righteouness, आश्रित्य having taken recourse, तिष्ठता by one who abides in, वाक्यम् words, वृथा in vain, न कर्तव्यम् is not to be done.

Any one, O hero, who has taken recourse to righteousness should not allow the promise made to his father, mother or a brahmin to go in vain.