15 Yesterday I handled the verse, “Day unto day utters speech,” as my ability enabled me; today holy Scripture seems to me not only to have prophesied in former times, but even at the present. For when I behold your holy celebration continued day and night, the oracles of the prophet's song have declared that these days, yesterday and today, are the days of which it is most opportunely said: “Day unto day utters speech;” and these the nights of which it is most fittingly said that “Night unto night shows knowledge.” For what else but the Word of God have you during these two days uttered with inmost affection, and have proved yourselves to have the knowledge of the faith.
Source: Letters (New Advent)