The Compendium of Caraka 3.8.8

3.8.8

athādhyāpanavidhiḥ---adhyāpane kṛtabuddhirācāryaḥ śiṣyamevāditaḥ parīkṣeta; tadyathā---praśāntamāryaprakṛtikamakṣudrakarmāṇamṛjucakṣurmukhanāsāvaṃśaṃ tanuraktaviśadajihvamavikṛtadantauṣṭhamaminminaṃ dhṛtimantamanahaṅkṛtaṃ medhāvinaṃ vitarkasmṛtisaṃpannamudārasattvaṃ tadvidyakulajamathavā tadvidyavṛttaṃ tattvābhiniveśinamavyaṅgamanyāpannevdriyaṃ nibhṛtam-*anuddhatamarthatattvabhāvakamakopanamavyasaninaṃ śīlaśaucācārānurāgadākṣyaprādakṣiṇyopapannamadhyayanābhikāmamarthavijñāne karmadarśane cānanyakāryamalubdhamanalasaṃ *sarvabhūtahitaiṣiṇamācāryasarvānuśiṣṭipratikaramanuraktaṃ ca, evaṃguṇasamuditamadhyāpyamāhuḥ//

Now the rule for teaching: a teacher who has resolved upon teaching should first examine the pupil, namely: peaceful, noble by nature, not engaging in base actions, with straight eyes, mouth, and bridge of the nose, with a thin, red, and clean tongue, with undeformed teeth and lips, not nasal-speaking, resolute, free from arrogance, intelligent, endowed with reasoning and memory, of noble temperament, born into a family of that science or observing the conduct of that science, devoted to the truth, devoid of deformity, with faculties not impaired, modest, not haughty, contemplating the true nature of things, free from anger, free from vices, endowed with character, cleanliness, good conduct, affection, competence, and dexterity, desirous of study, having no other business in understanding the meaning and observing practical work, ungreedy, not indolent, wishing the welfare of all beings, obedient to all instructions of the teacher, and affectionate—one who is endowed with such qualities, they say, is fit to be taught.