Sayyiduna Wathilah bin al-Asqa' (may Allah be pleased with him) says that the Messenger of Allah (peace and blessings be upon him) said: "Among the greatest of lies is that someone ascribes himself to someone other than his father, or makes his eyes see in a dream what they did not see, or attributes to Allah and His Messenger what they did not say."
Hadith Referenceالمعجم الكبير للطبراني / باب الواو / 18398