source document
noun1
An original document that is subsequently copied, translated, or transcribed.
2
An original document or record that provides proof of activity that is summarized elsewhere (e.g. case notes, medical chart, diary entry, minutes of a meeting, etc.).
3
Accounting, Business, Finance A document that provides official notification of a credit or debit to an account, such as a bank statement, bill of sale, invoice, receipt, etc.