Genesis 48:19-20

48:19 But his father refused and said, “I know, my son, I know. He too will become a nation and he too will become great. In spite of this, his younger brother will be even greater and his descendants will become a multitude of nations.” 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.