St. Benedict's Rule for Monasteries

From Easter until the Calends of November let the same number of Psalms be kept as prescribed above; but no lessons are to be read from the book, on account of the shortness of the nights. Instead of those three lessons let one lesson from the Old Testament be said by heart and followed by a short responsory. But all the rest should be done as has been said, that is to say that never fewer than twelve Psalms should be said at the Night Office, not counting Psalm 3 and Psalm 94.