Manava Dharmashastra 2.116

2.116

yo'bhyāsārthamadhīyānasyānyaṃ coddiśyaiva vyācakṣāṇasya tatsaṃnikarṣamanya āgatya tadbrahmāpūrva gṛhīyātsandehaṃ vā'panudettasyaiṣa doṣa ucyate | yāvadanujñāmasau na dāpyate | 'yathaite tvatsakāśādadhīyata evamahamapyadhīyīyetyanujñātumarhasīti' labdhānujñāṃ śikketa | anyathā tu yadbrahmādhyayanaṃ tatsteyamiva | so'dhyetā'nena brahmacauryeṇa saṃyukto narakaṃ mahāyayātanāsthānaṃ prāpnoti | adhīyānāditi pañcamī "ākhyātopayoge" ( pā.sū.1|

He, who may acquire Veda, without his permission, from one who is reciting it, becomes corrupted with the sin of stealing the Veda, and falls into hell.—(116)

Medhātithi’s commentary (manubhāṣya):
When one is reciting the Veda with a view to getting up the text, or when one is expounding the Veda to another person,—if some one were to come by and acquire the Vedic text for the first time, or should surreptitiously have bis own doubts (on some point connected with the Vedic text) removed,—then to him occurs the sin here described; so long as he does not secure the Teacher’s permission, preferring, his request in such words as—‘just as these pupils are reading with you, so may I also read, kindly accord me your permission.’ And it is only when the pupil has received this permission that he should be taught. Otherwise, the reading of the Veda would be like ‘stealing’; and the learner, being corrupted with this sin of stealing the Veda, falls into hell—i.e., into a place of condign punishment.

The ablative ending in ‘adhīyānāt,’ ‘from one who is, reciting it,’ is according to Pāṇini 1.4.29, according to which ‘the source of proper instruction is put in the Ablative’;—or the Ablative may have the sense of separation,—separation being implied by the fact that the teaching appears to issue from the Teacher;—or the Ablative may have the sense of the participle, being used in place of the affix ‘lyap,’ the meaning being—‘he learns after having heard another person who is reciting it.’—(116)

Comparative notes by various authors
Viṣṇu-Smṛti (30.42-43).—‘Until permitted by the Teacher, one should not acquire knowledge from another person who may be reading with the Teacher;—such acquisition of knowledge constitutes Veda-stealing and leads one to hell.’