The prophecy is that the Imam Mahdi will be revealed after a Ramadan with two (total?) eclipses. Ramadans with two eclipses are by no means rare, which is why there is so much emphasis on total eclipses. There's more to it than that - he will be hidden and revealed around that time or shortly thereafter, he will accept his role reluctantly and only after much persuasion, and so forth. Bin Laden appears all too eager for the role, this alone doesn't fit the prophecy.
The prophecy appears nowhere in the Koran. It is in some of the extra-Koranic texts known as the "Hadith" - this is roughly the Islamic equivalent of the Jewish Talmud or the Kabbalah, or some of the early Christian texts such as the "Shepherd of Hermes" or writings of some of the early Church fathers which were rejected for inclusion in the New Testament. The Hadith are sayings attributed to Mohammud but whose provenance is more dubious than those included in the Koran. Some Muslims consider them inspired and others reject them outright, and some accept only a few of them. The ones relating to the Mahdi are of disputed origin and veracity, even among the Islamic clerics.