Genesis 48:5
And now thy two sons, Ephraim and Manasseh, which were born unto thee in the land of Egypt before I came unto thee into Egypt, are mine; as Reuben and Simeon, they shall be mine. And now thy two sons, Ephraim and Manasseh, which were born unto thee in the land of Egypt before I came unto thee into Egypt, are mine; as Reuben and Simeon, they shall be mine.
The declaration belongs to the famine years, when seven years of scarcity pressed upon Canaan and ten of Jacob's sons journeyed to Egypt to purchase grain. There they bowed with their faces to the earth before Joseph, who stood as ruler of the land over the distribution. They did not know him, but he knew them, and as his youthful dreams returned to his mind he proved and tested them.
By it Joseph's two sons were formally set among the children of Israel, Ephraim and Manasseh being taken as Jacob's own, on the same standing as Reuben and Simeon, to become heads of distinct tribes. In this way Joseph received a double portion in Israel, for one of the birthright privileges forfeited by Reuben was transferred to him. The act revealed Joseph's faith in the covenant promise, since he thereby renounced for his sons all the honor and wealth and distinction that lay open to them through their mother's kinship with the highest order of the Egyptian priesthood and through their father's high position. He chose for them instead a lot with the despised shepherd tribes to whom the oracles of God had been entrusted.