Apastambadharmasutra 2.2.5

On the day on which, beginning the study of the whole sacred science, the Upanishads (and the rest, he performs the Upâkarma in the morning) he shall not study (at night).

And he shall not leave his teacher at once after having studied (the Veda and having returned home)

If he is in a hurry to go, he shall perform the daily recitation of the Veda in the presence of his teacher, and then go at his pleasure. In this manner good fortune will attend both of them.

If the (former) teacher visits him after he has returned home, he shall go out to meet him, embrace his (feet), and he shall not wash himself (after that act), showing disgust. He then shall let him pass first into the house, fetch (the materials necessary for a hospitable reception), and honour him according to the rule.

If his former teacher is) present, he himself shall use a seat, a bed, food, and garments inferior to, and lower (than those offered to the teacher.

Standing (with his body bent), he shall place his left hand (under the water-vessel, and bending with his other hand its mouth downwards), he shall offer to his teacher water for sipping.

And (he shall offer water for sipping in this manner) to other guests also who possess all (good qualities) together.

He shall imitate (his teacher) in rising, sitting, walking, about, and smiling.

In the presence (of his teacher) he shall not void excrements, discharge wind, speak aloud, laugh, spit, clean his teeth, blow his nose, frown, clap his hands, nor snap his fingers.

Nor shall he tenderly embrace or address caressing words to his wife or children.

He shall not contradict his teacher,

Nor any of his betters.

(He shall not) blame or revile any creature.

(He shall not revile one branch of) sacred learning by (invidiously comparing it with) another.

If he is not well versed in a (branch of) sacred learning (which he studied formerly), he shall again go to the (same) teacher and master it, observing the (same) rules as (during his first studentship).

The restrictions (to be kept) by the teacher from the beginning of the course of teaching to its end are, to avoid cutting the hair on the body, partaking of meat or of oblations to the Manes, and connection (with a woman).

Or (he may have conjugal intercourse) with his wife at the proper season.

He shall be attentive in instructing his pupils in the sacred learning, in such a manner that they master it, and in observing the restrictions (imposed upon householders during their teaching. He who acts thus, gains heavenly bliss for himself, his descendants and ancestors.

He who entirely avoids with mind, word, nose, eye, and ear the sensual objects (such as are) enjoyed by the touch, the organ, or the stomach, gains immortality.