Samurah (may Allah be pleased with him) reported that the Prophet (may Allah's peace and blessings be upon him) said: "Whoever reports a Hadīth on my authority that is thought to be false is one of the two liars (the one who fabricated it and the one who reported it). "
شرح الحديث :
This noble Hadīth warns against narrating anything on the authority of the Prophet (may Allah's peace and blessings be upon him) while knowing or thinking that what he is narrating is a lie about the Prophet (may Allah's peace and blessings be upon him). It warns him against doing that as he would be considered exactly like the one who intentionally lied about the Prophet.