According to numerous Islamic sources, Muhammad once delivered a revelation promoting polytheism. Later, he claimed that Satan had tricked him into delivering these infamous "Satanic Verses" (as they are now called). Here's the story, according to Ibn Ishaq's Sirat Rasul Allah (our earliest biographical source on Muhammad):
Now the apostle was anxious for the welfare of his people, wishing to attract them as far as he could. . . . When the apostle saw that his people turned their backs on him and he was pained by their estrangement from what he brought them from God he longed that there should come to him from God a message that would reconcile his people to him. Because of his love for his people and his anxiety over them it would delight him if the obstacle that made his task so difficult could be removed. . . . Then God sent down "By the star when it sets your comrade errs not and is not deceived, he speaks not from his own desire," and when he reached His words "Have you thought of al-Lat and al-Uzza and Manat the third, the other", Satan, when he was meditating upon it, and desiring to bring it to his people, put upon his tongue "these are the exalted Gharaniq [Numidian cranes] whose intercession is approved." When the Quraysh heard that, they were delighted and greatly pleased at the way in which he spoke of their gods and they listened to him; while the believers were holding that what their prophet brought them from their Lord was true, not suspecting a mistake or a vain desire or a slip, and when he reached the prostration and the end of the Sura in which he prostrated himself the Muslims prostrated themselves when their prophet prostrated confirming what he brought and obeying his command, and the polytheists of Quraysh and others who were in the mosque prostrated when they heard the mention of their gods, so that everyone in the mosque believer and unbeliever prostrated . . . Then the people dispersed and the Quraysh went out, delighted at what had been said about their gods, saying, "Muhammad has spoken of our gods in splendid fashion. He alleged in what he read that they are the exalted Gharaniq whose intercession is approved."
The news reached the prophet’s companions who were in Abyssinia, it being reported that Quraysh had accepted Islam, so some men started to return while others remained behind. Then Gabriel came to the apostle and said, "What have you done, Muhammad? You have read to these people something I did not bring you from God and you have said what He did not say to you." The apostle was bitterly grieved and was greatly in fear of God. So God sent down (a revelation), for He was merciful to him, comforting him and making light of the affair and telling him that every prophet and apostle before him desired as he desired and wanted what he wanted and Satan interjected something into his desires as he had on his tongue. So God annulled what Satan had suggested and God established His verses, i.e. you are just like the prophets and apostles. Then God sent down: "We have not sent a prophet or apostle before you but when he longed Satan cast suggestions in his longing. But God will annul what Satan has suggested. Then God will establish his verses, God being knowing and wise." (Ibn Ishaq, pp. 165-166)
Hmmm. So Muhammad, according to Muslim sources, couldn't tell the difference between a revelation from God and a revelation from Satan? Nothing to worry about here (unless you like to think).