The Law Code of Yājñavalkya 2.6.63

2.6.63

śuddham aśuddhaṃ veti saṃdigdhasya lekhyasya śuddhiḥ svahastalikhitādibhiḥ syāt | svahastena likhitaṃ yal lekhyāntaraṃ tena śuddhiḥ | yadi sadṛśāny akṣarāṇi bhavanti tadā śuddhiḥ syād ity arthaḥ | ādiśabdāt sākṣilekhakasvahastalikhitāntarasaṃvādāc chuddhir iti | yuktyā prāptir yuktiprāptiḥ | deśakālapuruṣāṇāṃ dravyeṇa saha saṃbandhaḥ prāptiḥ | asmin deśe 'sminkāle 'sya puruṣasyedaṃ dravyaṃ ghaṭata iti yuktiprāptiḥ | kriyā tatsākṣyupanyāsaḥ | cihnam asādhāraṇaṃ śrīkārādi | saṃbandho 'rthipratyarthinoḥ pūrvam api parasparaviśvāsena dānagrahaṇādisaṃbandhaḥ | āgamo 'syaitāvato 'rthasya saṃbhāvitaḥ prāptyupāyaḥ | ete eva hetavaḥ | ebhir hetubhiḥ saṃdigdhalekhyasya śuddhiḥ syād ity anvayaḥ | yadā tu lekhyasaṃdehe nirṇayo na jāyate tadā sākṣibhir nirṇayaḥ kāryaḥ | yathāha kātyāyanaḥ:

The clearing of a document that is doubtful as to whether it is genuine or ungenuine should be by handwriting and the like. It is cleared by another document written in his own hand; that is to say, if the characters are similar, then there is clearing. By the word "and the like" [is meant] clearing through the agreement of other documents written in the hand of the witnesses or the scribe. "Plausibility" is arrival through reasoning. "Probability" is the connection of place, time, and person with the wealth; plausibility means that it is plausible that this wealth belongs to this person in this place at this time. "Evidence" is the adducing of witnesses to it. "Mark" is an uncommon sign, such as the invocation śrī or the like. "Association" is the prior relationship between the plaintiff and defendant through mutual trust, such as giving and taking. "Title" is the probable means of acquisition of this much wealth. These are indeed the grounds. The syntax is: by these grounds, the clearing of a doubtful document should take place. But when a determination does not arise in the case of doubt regarding a document, then the determination must be made by witnesses. As Kātyāyana says: