What is the origin of the Prophet's saying, peace be upon him, to Ali: "Indeed, the seller is Jibreel, and the buyer is Mika'eel"?

If the story the questioner is asking about is the one concerning Ali selling Fatimah's Izar (garment) and donating its price, and then selling a she-camel to Gabriel, who appeared in the form of a human, then it is a fabricated story with no basis. Al-Halabi narrated in his Sīrah (biography) from Al-Suyuti that Al-Suyuti was asked about this story and he said: "It is among the fabricated lies."