Kautilya's Arthashastra 1.3.10

1.3.10

brahmacāriṇaḥ svādhyāyo agnikāryābhiṣekau bhaikṣavratitvam ācārye prāṇāntikī vṛttis tadabhāve guruputre sa-brahmacāriṇi vā //

That of a student (Brahmacharin) is learning the Vedas, fire-worship, ablution, living by begging, and devotion to his teacher even at the cost of his own life, or in the absence of his teacher, to the teacher's son, or to an elder classmate.