Mahabharata 12.234.16

आयुषस्तु चतुर्भागं ब्रह्मचार्यनसूयकःगुरौ वा गुरुपुत्रे वा वसेद्धर्मार्थकोविदः

āyuṣastu caturbhāgaṃ brahmacāryanasūyakaḥgurau vā guruputre vā vaseddharmārthakovidaḥ

Our plain-language meaning of this verse is waiting for scholar review.