Provided are a computer program product, system, and method for indicating a sending buffer and receiving buffer in a message to use to validate the message in the receiving buffer. A receiving node includes a receive buffer for each of a plurality of external adaptors in external nodes. The receive buffers store messages from the external adaptors. Each of the messages includes an indicated receiving adaptor to receive the message and an indicated sending adaptor that sends the message. A determination is made as to whether the sending adaptor that sent the message comprises the indicated sending adaptor and that a receiving adaptor that received the message comprises the indicated receiving adaptor. An error is indicated for the message in response to determining that at least one of the sending and receiving adaptors that sent and received the message, respectively do not comprise the indicated sending and receiving adaptors, respectively.