Canto 2 -
Ayodhyā-kāṇḍa
Chapter 34: Rāma, Lakṣmaṇa and Sītā Meet Daśaratha
Text 2.34.48

त्वामहं सत्यमिच्छामि नानृतं पुरुषर्षभ।
प्रत्यक्षं तव सत्येन सुकृतेन च ते शपे॥

tvām ahaṁ satyam icchāmi nānṛtaṁ puruṣa-rṣabha
pratyakṣaṁ tava satyena sukṛtena ca te śape

tvām = you; aham = I; satyam = to make truthful; icchāmi = want; na = not; anṛtam = and untruthful in speech; puruṣa-rṣabha = O king; pratyakṣam = in presence; tava = your; satyena = on truth; sukṛtena = piety; ca = and; te = you; śape = I promise this.

I want to make you truthful and not untruthful in speech, O king.1 In your presence, I promise you this on truth and piety. 

1]. Rāmāyaṇa-bhāva-dīpa: satyaṁ satya-bhāṣiṇam tvāṁ nānṛtam ananṛta-bhāṣiṇam kartum icchāmi.