The Law Code of Yājñavalkya 3.1.46

3.1.46

ādiṣṭī brahmacāry asy apo 'śāna karma kuru divā mā svāpsīḥ (ĀśGṛ 1.22.2) ityādivratādeśayogād brahmayacāry ucyate | etac ca pitrādivyatirekeṇeti vakṣyati, ācāryapitrupādhyāyān iti (YDh 3.15) | ātrācāryaḥ punar evaṃ manyate ādiṣṭīti prakāntaprāyaścittaḥ kathyate tasyaivāyam udakadānādiniṣedhaḥ prāyaścittarūpavratasya samāptyuttarakālam udakadānāśaucavidhir iti | tathā klībādīnāṃ codakadāyitvaṃ niṣiddham,

'One under a vow' means a student of the Veda; he is called a student of the Veda because of the connection with the injunction of vows such as: 'You are a student of the Veda; sip water; do your duty; do not sleep by day' (ĀśGṛ 1.22.2). And he will state that this is with the exception of the father and others, in the verse: '[Except for] teachers, fathers, and instructors' (YDh 3.15). But the teacher here, on the other hand, considers thus: by the word 'one under a vow', one who has commenced a penance is spoken of; this prohibition of the water offering and the like applies only to him, and the rule regarding the water offering and ritual impurity applies to the time after the completion of the vow in the form of a penance. Likewise, being an offerer of water is prohibited for eunuchs and others, in accordance with the Smṛti of Vṛddha-Manu: