Berakhot

The fact is, said Raba, that the benediction is said first and then the loaf is broken.  The Nehardeans acted as prescribed by R. Hiyya, while the Rabbis acted as prescribed by Raba. Rabina said: Mother told me: Your father acted as prescribed by R. Hiyya; for R. Hiyya said: The bread should be broken with the conclusion of the blessing, whereas the Rabbis acted as prescribed by Raba. The law is as laid down by Raba, that one says the blessing first and afterwards breaks the loaf. It has been stated: If pieces and whole loaves are set before one, R. Huna says that the benediction can be said over the pieces,  and this serves also for the whole loaves, whereas R. Johanan says that the religious duty is better performed if the blessing is said over the whole one. If, however, a broken piece of wheat bread and a whole loaf of barley bread are set before one, all agree that the benediction is said over the piece of wheaten bread, and this serves also for the whole loaf of barley bread. R. Jeremiah b. Abba said: There is the same difference of opinion between Tannaim:  Terumah is given from a small whole onion, but not from the half of a large onion. R. Judah says: Not so, but also from the half of a large onion.  Are we to say that the point in which they differ is this: one authority holds that the fact of being worth more is more important, while the other holds that the fact of being whole is more important? — Where a priest is on the spot,  all agree that the fact of being worth more is more important. Where they differ is when there is no priest on the spot, since we have learnt: Wherever a priest is on the spot, terumah is given from the best of the produce; where the priest is not on the spot,  terumah is set aside from that which will keep best. R. Judah said: Terumah is in all cases given from the best.  R. Nahman b. Isaac said: A Godfearing man will seek to satisfy both.  Who is such a one? Mar the son of Rabina. For Mar the son of Rabina used to put the broken piece under  the whole loaf and then break the bread.  A Tanna recited in the presence of R. Nahman b. Isaac: One should place the broken piece under the whole loaf and then break and say the benediction. He said to him: What is your name? Shalman, he replied. He said to him: Thou art peace [shalom] and thy Mishnah is faultless [shelemah], for thou hast made peace between the scholars. R. Papa said: All admit that on Passover one puts the broken cake under the whole one and breaks [them together]. What is the reason? Scripture speaks of 'Bread of poverty'.  R. Abba said: On Sabbath one should break bread from two loaves. What is the reason? Scripture speaks of 'double bread'.  R. Ashi said: I have observed R. Kahana take two and break one. R. Zera used to break off [a piece of bread] sufficient for the whole meal [on Sabbath]. Said Rabina to R. Ashi: Does not this look like greediness? He replied: Since every other day he does not act thus and today he acts thus, it does not look like greediness. When R. Ammi and R. Assi happened to get hold of a loaf which had been used for an 'erub,  they used to say over it the blessing, 'who bringest forth bread from the earth', saying, Since one religious duty has been performed with it, let us perform with it still another.