Several websites (for example, here and here) report the story that kefir grains, which are used in the making of the fermented milk drink kefir, were given to Orthodox Christians in the Northern Caucasus by the Prophet Mohammed. According to the first of those sources, the legend is still current among Muslims who live in that region.
In one version, the tradition is that Mohammed prohibited the further dissemination of the grains, saying it would cause a loss of their magical powers.
On the face of it, the story that the founder of Islam gave such a special gift to Orthodox Christians is remarkable. But I found no traces of it dating to before the present century. What is its origin?