Though in How to Eat to Live he never precisely says why, Muhammad lists most legumes—lima beans, field peas, black-eyed peas, speckled peas, red peas, and brown peas—as among the divinely prohibited. The navy bean was the sole exception.
These rules, he wrote, came directly from the mouth of Wallace Fard Muhammad, who the protege asserted came to Detroit from Mecca to found the Nation of Islam (and then mysteriously disappeared en route to Chicago in 1934). And with him came the recipe for bean pie, according to Lance Shabazz, an archivist and historian of the Nation who says that the theory of the bean pie emerging as a substitute for sweet potato pie might have some validity. Elijah Muhammad doesn’t mention bean pie, but he’s pretty clear about sweet potatoes: “Sweet potatoes were never good for any human to eat. They are good for hogs, but not for you.” (That might have been a tough sell for African-Americans new to the Nation. Sweet potato pie, which originated in the south, was likely the mingling of the cooking of African slaves, who knew yams, and their European masters, who knew pie crust. It is enshrined in the soul food canon.)
In any case, Lance Shabazz says Fard Muhammad bestowed the first recipe for bean pie upon Elijah Muhammad and his wife, Clara, in the 30s in Detroit, though none of this is precisely stated in How to Eat to Live either.
But bean pie is in fact a convincing substitute for sweet potato pie. Built on a whole-wheat crust, with a filling of strained and mashed beans, butter, raw sugar, evaporated milk, eggs, cinnamon, and other baking spices, it develops a mildly sweet, dense, custardy understory, with a browned layer on top that one bean pie maker told me is the result of the butter rising and browning in the heat of the oven. If nobody tipped you off to the fact that you were eating pie made from mashed navy beans, you could be forgiven for thinking it was sweet potato or pumpkin pie.