This is a statement of everyday thermodynamic equilibrium with the environment, and no citation is needed.
The claim states that bread remains warm at room temperature due to ongoing thermodynamic processes. This is a basic matter of everyday thermal equilibrium and thermodynamics (objects sharing the same ambient temperature are in thermal equilibrium). Per Step 0 of the instructions, statements that are trivially true by direct everyday observation or physical definition are classified as common knowledge, requiring no citation.