The Weird Sisters came directly from Shakespeare's source material for the play, Raphael Holinshed's "Chronicles of England, Scotland and Ireland".
"It fortuned as Makbeth and Banquho iournied towards Fores, where the king then laie, they went sporting by the waie togither without other companie, saue onelie themselues, passing thorough the woods and fields, when suddenlie in the middest of a laund, there met them thrée women in strange and wild apparell, resembling creatures of elder world, whome when they attentiuelie beheld, woondering much at the sight, the first of them spake and said; 'All haile Makbeth, thane of Glammis' (for he had latelie entered into that dignitie and office by the death of his father Sinell.) The second of them said; 'Haile Makbeth thane of Cawder.' But the third said; 'All haile Makbeth that héerafter shalt be king of Scotland.'"
I don't know anything about the source materials Holinshed used to create his work. But given their presence together -- with one speaking of the past, another of the present (though at that moment MacBeth does not know he has been made Thane of Cawdor), and the third of the future -- it seems likely enough that in the original of the story the three women represented Urðr, Verðandi, and Skuld, the Norns of Norse myth. Large parts of northern Scotland and northeastern England were Viking realms during the lifetime of the historical MacBeth, so it's not at all implausible that they might figure in stories deriving from that time.