diff --git a/src/content/docs/concepts/payload.md b/src/content/docs/concepts/payload.md
index 6b1e564..877c1e2 100644
--- a/src/content/docs/concepts/payload.md
+++ b/src/content/docs/concepts/payload.md
@@ -6,5 +6,6 @@ sidebar:
 
 [Processors](/concepts/Processors) operator on a "wrapped" version of the message produces by the module. This wrapped version is available to all processors and is defined as follows:
 - **Payload**: the actual message produced by the module (or the result of the previous [processor](/concepts/processors) in the [route](/concepts/routes)).
+- **Source**: the id of the module that produced the original payload.
 - **Sender**: the network address of the module that produced the message (if applicable not all modules will have a sender address).
 - **Modules**: a map of all [modules](/concepts/modules) in the router with the module id as the key and the module instance as the value.