Gita was spoken by God as an essence of vedas around 3102+30=3430 BC , Vedas DO NOT have an author. They are transmitted through oral tradition by brahmanas for millions of years and then penned down by Veda Vyasa atleast around 7000 BC fearing the loss of them. Vedas are ordinances, do this and do not do this, and lay the metaphysical aspects of universe. They do not talk about prophecies/ fairy tales/ triple talAq :| and so on........So there you go.
Bhavishya purana was heavily tampered by britishers when they ruled India/ Bhaarat, and it is not an authentic purana to start with. Even then I heard that muhammad is predicted as evil in it.
Then, as verses 7-8 relate, the Aryan King Bhojaraja, who had already left India for the lands across the Sindhu River and to the west, meets Mahamada [some say this is Mohammed], the preceptor of the mleccha-dharma [religion of the mlecchas], who had arrived with his followers. Thereafter, however, the King went to worship the image of Lord Mahadev, the great god Shiva, situated in the marusthal, desert. King Bhoj bathed the image of Shiva with Ganges water and worshiped him in his mind with panchagavya (the five purificatory elements from the cow, consisting of milk, ghee, yogurt, cow dung, and cow urine), along with sandalwood paste, etc., and offered him, the image of Shiva, sincere prayers and devotion. King Bhoj prayed to Lord Mahadev, "O Girijanath who stays in the marusthal (land of deserts), I offer my prayers to you. You have forced maya [the illusory energy] to destroy Tripurasur [the demon Tripura]; but the mlecchas are now worshiping you. You are pure and sat-chit-anand swaroop [eternal knowledge and bliss]. I am your sevak [servant]. I have come under your protection."
Verses 10-27 relates next that Suta Goswami explained: After hearing the king’s prayers and being pleased with him, Lord Shiva said: "Let the King go to Mahakaleshwar (Ujjain) in the land of Vahika, which is now contaminated by mlecchas. O King, the land where you are standing, that is popular by the name of Bahik, has been polluted by the mlecchas. In that terrible country there no longer exists Dharma. There was a mystic demon named Tripura (Tripurasura), whom I have already burnt to ashes once before, he has come again by the order of Bali. He has no origin but he achieved a benediction from me. His name is Mahamada and his deeds are like that of a ghost. Therefore, O king, you should not go to this land of the evil ghost. By my mercy your intelligence will be purified." [This would seem to indicate that this Mahamada was an incarnation of the demon Tripura.] So hearing this, the king came back to his country and Mahamada came with them, but only to the bank of the river Sindhu. He was expert in expanding illusion, so he said to the king very pleasingly, "O great king, your god has become my servant. Just see, as he eats my remnants, so I will show you."
The king became surprised when he saw this happening before them. Then in anger Kalidasa, the king’s commander, rebuked Mahamada, "O rascal, you have created an illusion to bewilder the king, I will kill you, you are the lowest..." Then the king left that area.
Later, in the form of a ghostly presence, the expert illusionist Mahamada appeared at night in front of King Bhojaraja and said: "O King, your religion is of course known as the best religion among all. Still, by the order of the Lord, I am going to establish a terrible and demoniac religion and enforce a strong creed over the meat-eaters [mlecchas]. My followers will be known by their cut [circumcised] genitals, they will have no shikha [tuft of hair on their head, like Brahmanas], but will have a beard, make noise loudly, and eat all kinds of animals except swine without observing any rituals. They will perform purificatory acts with the musala, and thus be called musalman, and not purify their things with kusha grass [one of the Vedic customs]. Thus, I will be the originator of this adharmic [opposed to Vedic or Aryan Dharma] and demoniac religion of the meat-eating nations." After having heard all this, the Bhavishya Purana goes on to relate that King Bhojaraja returned to his land and palace, and that ghost of the man also went back to his own place.