Genesis 48:5, 13-14, 18-20

Now your two sons [Ephraim and Manasseh], who were born to you in the land of Egypt before I came to you in Egypt, are mine; Ephraim and Manasseh shall be mine [that is, adopted as my heirs and sons as surely], as Reuben and Simeon are my sons.

Then Joseph took them both, Ephraim with his right hand toward Israel’s left, and Manasseh with his left hand toward Israel’s right, and brought them close to him. But Israel reached out his right hand and laid it on the head of Ephraim, who was the younger, and his left hand on Manasseh’s head, crossing his hands [intentionally], even though Manasseh was the firstborn.

Joseph said to his father, “Not so, my father, for this is the firstborn; place your right hand on Manasseh’s head.” But his father refused and said, “I know, my son, I know; Manasseh also will become a people and he will be great; but his younger brother shall be greater than he, and his descendants shall become a multitude of nations.” Then Jacob blessed them that day, saying, “By you Israel will pronounce a blessing, saying, ‘May God make you like Ephraim and Manasseh.’ ” And he put Ephraim before Manasseh.