Reference for Taanit 4:1

בִּשְׁלשָׁה פְרָקִים בַּשָּׁנָה כֹּהֲנִים נוֹשְׂאִין אֶת כַּפֵּיהֶן אַרְבַּע פְּעָמִים בַּיּוֹם, בַּשַּׁחֲרִית, בַּמּוּסָף וּבַמִּנְחָה וּבִנְעִילַת שְׁעָרִים, בַּתַּעֲנִיּוֹת וּבַמַּעֲמָדוֹת וּבְיוֹם הַכִּפּוּרִים:

At three periods of the year, the priests shall raise their hands [to bless the people], in each prayer, [and] four times [in one of them], in the morning, additional, afternoon, and closing [or concluding] prayers. [The three mentioned periods are] on the fast-days, on the fast of the standing men, and on the day of atonement.

Jastrow