Is the circulating hadith on social media, which prohibits the "interbreeding of knuckles," authentic?

The Hadith prohibiting the intermingling of the barājim has no basis.

Al-Barājim refers to the joints or knuckles of the fingers where dirt collects. Most scholars are of the opinion that they are the knuckles on the back of the hand.

Washing the barājim is part of the fitra (innate disposition), as it is authentically reported in the Hadith of Aisha regarding the Prophet, peace and blessings be upon him: "Ten things are part of the fitra: ...and washing the barājim..."