Is he sinful who said about the sender of a message containing the two declarations of faith and a threat of removal from Messenger if it is not sent: "This one exaggerated in his words"?

The questioner incurs no sin by uttering this with this intention, as he suffers from severe waswasah (whispers/obsessive thoughts) concerning purity and matters of disbelief. The cure for this lies in striving against oneself to cut off these thoughts and turn away from them.