The Law Code of Yājñavalkya 2.6.2

2.6.2

lekhyaṃ tu dvividhaṃ jñeyaṃ svahastānyakṛtaṃ tathā |
asākṣimat sākṣimac ca siddhir deśasthites tayoḥ ||
iti | (NSm 1.115)

"A document, however, should be known as twofold: handwritten by oneself, and likewise written by another; / without witnesses and with witnesses; their validity arises from the established custom of the country." / So it is. (NSm 1.115)