Valmiki Ramayana Sundara Kanda Sarga 33 Shloka 21

नृपतिसत्तम the foremost among kings, त्वया by you, प्रीत्या lovingly, यत् such, तत् वाक्यम् words, उक्तम् spoken, तत् the same, वितथम् false, न कार्यं that promise, यदि if you please, राघवः Rama, वनम् to the forest, गच्छतु go.

'O Dasaratha, the foremost among kings if the promise lovingly made by you earlier is not going to be false, Rama should go to the forest'.