Canto 1 - Boyhood
Bāla-kāṇḍa
Chapter 72: Daśaratha’s Charity Before the Wedding
Text 1.72.15
परो धर्मः कृतो मह्यं शिष्योऽस्मि भवतोः सदा॥
paro dharmaḥ kṛto mahyaṁ śiṣyo ’smi bhavatoḥ sadā
paraḥ dharmaḥ kṛtaḥ mahyam = you have caused me to perform a great activity of dharma; śiṣyaḥ asmi bhavatoḥ sadā = I will always be a disciple of both of you.
You have caused me to perform a great activity of dharma. I will always be a disciple of both of you.
The great activity of dharma that King Janaka is referring to is giving his daughters in charity.