Talmud Bavli Sotah on a Congregation Full of Kohanim

"Adda said in the name of Rabbi Simlai: In a synagogue whose attendance consists entirely of Kohanim, they all ascend the platform to recite the Blessing. One must wonder about Rabbi Simlai's statement: To whom, then, is their Blessing addressed, if there is no one else present among the congregation to receive the Blessing?"

-- Talmud Bavli, Sotah 38b

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

Talmud Yerushalmi Berachot on the Kohanic Blessing

"Rabbi Huna said: Regarding one who is in the presence of the Kohanim when they impart the three Kohanic blessings in the synagoge - when they recite the first blessing, he should say the verse 'Bless YHVH, O His angels, the strong warriors who do His bidding, to obey the voice of His word' (Psalms 103:20). When they recite the second blessing, he should say the verse 'Bless YHVH, all His legions, His servants who do His will' (Psalms 103:21). When they recite the third blessing, he should say the verse 'Bless YHVH, all His works, in all the places of His dominion; bless YHVH, O my soul' (Psalms 103:22).

-- Talmud Yerushalmi, Berachot 5a