Srimad-Bhagavatam: Canto 6 - Chapter 1 - Verse 28
Sanskrit:
पुत्राणां हि परो धर्म: पितृशुश्रूषणं सताम् ।अपि पुत्रवतां ब्रह्मन् किमुत ब्रह्मचारिणाम् ॥ २८ ॥
ITRANS:
putrāṇāṁ hi paro dharmaḥpitṛ-śuśrūṣaṇaṁ satāmapi putravatāṁ brahmankim uta brahmacāriṇām
Translation:
O brāhmaṇa, the highest duty of a son, even though he has sons of his own, is to serve his parents, and what to speak of a son who is a brahmacārī?