Manava Dharmashastra 6.29

6.29

etā dīkṣā niyamānanyāṃścāntarjalasthānacakṣurnimīlanādikaṃ seveta | śrutīraupaniṣadīḥ rahasyādhikārapaṭhitāni vedavākyāni adhīyīta cintayedbhāvayecca 'ātmasaṃsiddhaye' | brahmaprāptyarthaṃ vā upāsanā uktāḥ | vividhā ityanuvādaḥ |

Medhātithi’s commentary (manubhāṣya):
These ‘restraints’—observances and ‘others’—such as standing in water, keeping the eyes closed and so forth.

‘Vedic texts contained in the Upaniṣads.’—He shall study the texts contained in the esoteric sections of the Veda, and think of them and ponder over them;‘in order to attain the Self’.

Or this may refer to the several forms of worship that have been laid down for attaining Brahman.

‘Several’—this is a mere re-iteration.—(29).