Ramayana — Bala Kanda, Sarga 21, Shloka 8
बालकाण्डे एकविंशः सर्गः
Daśaratha’s Promise, Vasiṣṭha’s Counsel, and Viśvāmitra’s Weapon-Lore
संश्रुत्यैवं करिष्यामीत्यकुर्वाणस्य राघव।इष्टापूर्तवधो भूयात्तस्माद्रामं विसर्जय।।।।
saṃśrutyaivaṃ kariṣyāmīty akurvāṇasya rāghava |
iṣṭāpūrtavadho bhūyāt tasmād rāmaṃ visarjaya ||
ラ―ガヴァよ、「そういたします」と誓っておきながら果たさぬ者は、祭祀と布施の功徳を失う。ゆえにラーマを（聖仙と共に）送り出しなさい。
O Dasaratha, a promise made and not kept amounts to destruction of merits earned through previous pieties. Therefore send Rama (with him).
FAQs
Satya (keeping one’s pledged word) is dharma; breaking a promise is portrayed as spiritually destructive, nullifying accumulated religious merit.
Vasiṣṭha presses Daśaratha to honor his commitment to Viśvāmitra by sending Rāma, warning of the moral and ritual consequences of failing one’s promise.
Truthfulness and reliability (satya-niṣṭhā): a king’s word must be unwavering.