Genesis 48:4-5

48:4 He said to me, ‘I am going to make you fruitful and will multiply you. I will make you into a group of nations, and I will give this land to your descendants as an everlasting possession.’

48:5 “Now, as for your two sons, who were born to you in the land of Egypt before I came to you in Egypt, they will be mine. Ephraim and Manasseh will be mine just as Reuben and Simeon are.

Genesis 48:13-14

48:13 Joseph positioned them; he put Ephraim on his right hand across from Israel’s left hand, and Manasseh on his left hand across from Israel’s right hand. Then Joseph brought them closer to his father. 48:14 Israel stretched out his right hand and placed it on Ephraim’s head, although he was the younger. Crossing his hands, he put his left hand on Manasseh’s head, for Manasseh was the firstborn.

Genesis 48:20

48:20 So he blessed them that day, saying,

“By you will Israel bless, saying,

‘May God make you like Ephraim and Manasseh.’”

So he put Ephraim before Manasseh.