Valmiki Ramayana Ayodhya Kanda Sarga 42 Shloka 2

राजा king, प्रियम् beloved, अत्यन्तधार्मिकम् exceedingly virtuous, पुत्रम् son, यावत् as long as, पश्यति was able to see, तावत् so long, अस्य his, पुत्रदर्शने for the sight of the son, धरण्याम् the dust on the earth, व्यवर्धतेव appeared growing.

So long as king Dasaratha was able to see his exceedingly virtuous and beloved son (Rama), it appeared that his body kept rising from the earth to have a sight of his son.