Midrasz do Rodzaju 48:4

(Fol. 5b) Now let us see, whence do both R. Juda and R. Simon deduce that one tribe is also called Kahal (congregation)? From the following passage (II Chron. 20, 5) And Jehoshaphat stood forward in the Kahal of Judah and Jerusalem. R. Acha b. Jacob raised the following objection: "Perhaps there it was Kahal, because the tribe Benjamin, too, was there, hence more than one tribe? Therefore," said R. Acha b. Jacob, "it is inferred from the following (Gen. 48, 4) And I will make of thee a Kahal of people; now, at that time, Benjamin had not yet been born, and the Almighty said to Jacob: One Kahal more is born to you [referring to Benjamin]." Said R. Sheba to R. Cahana: "Perhaps the Holy One, praised be He! meant, now as Benjamin is born, and you have twelve tribes you are called Kahal?" Whereupon R. Cahana replied: "Do you mean to say that only twelve tribes are called Kahal, but eleven tribes are not called Kahal?

R. Acha b. Jacob said: "The tribe of Levi is not called Kahal at all, as from the abovecited verse (Ib. ib. 12) it is to be understood that only those who inherited landed property in the land of Israel are called a tribe, but not the Levites, who had no such inheritance." But if so then there are less than twelve tribes? Said Abaye: "It reads there (Ib.) that Ephraim and Manashah (the two sons of Joseph) are considered as Reuben and Simon; hence there is another tribe which completes the number."

R Samuel b. Nachmeini said in the name of R. Jonathan: "Whoever says that Reuben (the son of Jacob) sinned, errs, for it is said (Gen. 35, 22.) Now the sons of Jacob were twelve. It is intended to inform us that they were all equal [in righteousness]. How then shall we explain the first part of the above-mentioned passage? It is intended to teach that he (Reuben) deranged his father's bed, and the Scriptures charge him as if he had been lying with Bilhah." We are taught that R. Simon h. Elazar said: "That righteous one (Reuben) is cleared of that crime, that such an occurrence never happened to him, for how could it possibly be that a man whose descendants were to stand on Mt. Ebal and proclaim (Deu. 29, 20.) Cursed be he who lieth with his father's wife, would commit such a sin. But how then is the passage (Gen. 35, 22 ) And he lay with Bilhah, his father's concubine, to be explained? It is intended to inform us that he demanded redress for the humiliation inflicted upon his mother saying: 'When my mothers sister lived and proved a vexation to her, it was bearable; but that the servant of my mother's sister should be a vexation to my mother is unbearable!' Whereupon he went and deranged the bed of Bilhah." Others say he deranged two beds, that of the Schechina and that of his father, and this explains that which is written (Gen. 48, 4.) Unstable as water, thou shalt not have the excellence, because thou did go up to thy father's bed; then didst thou defile the Shechina of my couch. Do not read Yetzu'ey (my bed), but read Yetzuay (the beds).