Daniel 6

Daniel 6:10

And so in the monasteries of Palestine and Mesopotamia and all the East the services of the above-mentioned hours are ended each day with three psalms apiece, so that constant prayers may be offered to God at the appointed times, and yet, the spiritual duties being completed with due moderation, the necessary offices of work may not be in any way interfered with: for at these three seasons we know that Daniel the prophet also poured forth his prayers to God day by day in his chamber with the windows open. Nor is it without good reasons that these times are more particularly assigned to religious offices, since at them what completed the promises and summed up our salvation was fulfilled. For we can show that at the third hour the Holy Spirit, who had been of old promised by the prophets, descended in the first instance on the apostles assembled together for prayer. — INSTITUTES 3:3