Which of the following is considered a source document in an accounting system?

A source document in an accounting system refers to any original document that provides evidence of a financial transaction or an event. These documents are crucial as they serve as the basis for recording entries into accounting systems and financial statements.

Time cards are a prime example of a source document because they provide tangible evidence of the hours worked by employees, which directly impacts payroll calculations and labor cost tracking. This information is critical for accurately processing payroll and for labor cost analysis.

Invoices and bank statements, while also essential in the accounting process, serve slightly different purposes. Invoices are used for billing purposes, serving as requests for payment and reflecting sales transactions. Bank statements provide a summary of a company's financial activities within a banking period and are more of a record-keeping tool rather than a source document.

Balance sheets are financial statements summarizing an entity's assets, liabilities, and equity at a specific point in time. While they are essential for understanding a company's financial health, they do not qualify as source documents since they do not originate from the initial accounting transactions but rather are prepared after accounting records have been created from various source documents.

Thus, time cards serve as a primary source document in the accounting process by facilitating the accurate recording of labor costs related to employee work hours.