Adding reference to Journal Entry
To link a Journal Entry to the document* of choice, expand the row you want to insert a reference with and choose the Reference Type and Reference Name.
Refer to the GIF to illustrating the same:
List of Documents one can link to a Journal Entry:
Sales Invoice, Purchase Invoice, Journal Entry, Sales Order, Purchase Order, Expense Claim, Asset, Loan, Payroll Entry, Employee Advance, Exchange Rate Revaluation, Invoice Discounting, Fees.