Mishnah Sotah on the Kohanic Blessing

"How is the Kohanim's Blessing pronounced? In the provinces, the Kohen pronounces it as three blessings, but in the Temple he pronounces it as one blessing. In the Temple, the Kohen pronounces the Name of God as it is written, but in the provinces he expresses it with its alternative pronunciation. In the provinces, the Kohanim raise their hands to should height while reciting the blessing, but in the Temple they raise their hands above their heads, except the Kohen Gadol, who does not raise his hands above the tzitz. But Rabbi Yehudah says: Even the Kohen Gadol raises his hands above the tzitz. We learn that the Kohanim are required to raise their hands for it is stated: 'And Aaron raised his hands toward the people and he blessed them' (Leviticus 9:22)."

-- Mishnah, Sotah 7.6