The Artscroll Rishonim history book, in the section about the Rambam, records a "tradition" that the Rambam, as a young child, received a blessing from the Ri Migash, and that he (the Rambam) later attributed all of his accomplishment in Torah scholarship to that blessing.
Is there a recorded source for this "tradition," preferably within some reasonable time of the Rambam's era (let's say, pre-1350)?