Deuteronomy 33:17

His glory is like the firstling of his bullock, and his horns are like the horns of unicorns, of the fierce wild-ox; he would occupy a position of such power as to be able to trample on all his enemies; with them he shall push the people together to the ends of the earth; and they are the ten thousands of Ephraim, and they are the thousands of Manasseh. The power of Ephraim especially, but also of Manasseh, was afterwards such as to give to the tribe of Joseph the leadership in the northern nation.