In Genesis 48, Joseph receives word that his father Jacob is ill, so he takes his two sons, Manasseh and Ephraim, to visit him. Jacob, now old and blind, is informed of Joseph's arrival. Jacob musters his remaining strength and sits up in bed once more. Joseph positions his sons before Jacob so that the elder, Manasseh, is on Jacob's right side, and the younger, Ephraim, is on the left. He does this with the intention of receiving Jacob's blessing, following the custom of primogeniture from Jacob’s bed (where the firstborn receives a special blessing).
However, Jacob, guided by God's inspiration, crosses his hands, placing his right hand on Ephraim (the younger) and his left hand on Manasseh (the elder). When Joseph notices this, he tries to correct Jacob, but Jacob insists that he knows what he is doing to his brothers. He prophesies that Ephraim will become greater than Manasseh.
Joseph accepts Jacob's decision and Jacob proceeds to bless Ephraim and Manasseh, adopting them as his own sons, thereby giving them a share in his inheritance along with Jacob's other sons. Joseph is initially concerned about this reversal of the blessing, but Jacob reassures him that it is intentional, based on God's new plan.