Kautilya's Arthashastra 3.1.12

3.1.12

ato 'nyathā na sidhyeyuḥ, apāśrayavadbhiś ca kṛtāḥ, pitṛmatā putreṇa, pitrā putravatā, niṣkulena bhrātrā, kaniṣṭhenāvibhaktāṃśena, patimatyā putravatyā ca striyā, dāsāhitakābhyām, aprāptātītavyavahārābhyām, abhiśastapravrajitanyaṅgavyasanibhiś ca, anyatra niṣṛṣṭavyavahārebhyaḥ //

Such agreements (i.e., those entered into in seclusion, etc.) except as detailed above shall be void.

So also agreements entered into by dependent or unauthorised persons, such as a father's mother, a son, a father having a son, an outcast brother, the youngest brother of a family of undivided interests, a wife having her husband or son, a slave, a hired labourer, any person who is too young or too old to carry on business, a convict (abhisasta), a cripple, or an afflicted person, shall not be valid. But it would be otherwise if he were authorised.