Council of Trent: Session XXIII, Reformation, Chapter XIII

CHAPTER XIII. On the conditions required in the Ordination of a Subdeacon and Deacon: on no one shall two sacred Orders be conferred on the same day.

Such as have a good testimonial, and have been already tried in minor orders, and are instructed in letters, and in those things which belong to the exercise of their orders, shall be ordained subdeacons and deacons. They shall have a hope, with God's help, to be able to live continently; they shall serve in the churches to which they may be assigned; and are to know that it is very highly becoming that, after ministering at the altar, they should receive the sacred communion, at least on the Lord's days and solemnities. Those who have been promoted to the sacred order of the subdeaconship shall not, until they have remained therein during at least a year, be permitted to ascend to a higher degree, unless the bishop shall judge otherwise. Two sacred orders shall not be conferred on the same day, even upon Regulars; any privileges and indults whatsoever, to whomsoever granted, to the contrary notwithstanding.

Translation: J. Waterworth, The Canons and Decrees of the Council of Trent (1848), Hanover Historical Texts Project transcription (1995).