Tetzel: "For every mortal sin a man commits he must, after making a good confession, suffer seven years in purgatory, unless he has done seven years penance"

Here's one from the mailbox:

Hi James. I hope this email reaches you. I am a PhD student in History.  I am frantically searching for the source of this letter, written by John Tetzel:

Tell your people,” he wrote, “that for every mortal sin a man commits he must, after making a good confession, suffer seven years in purgatory, unless he has done seven years penance. Bid them think how many mortal sins a day are committed, how many each week, each month, each year. All but infinite, then, are the pains they must undergo in the flames of purgatory. This indulgence will mean for them full remission of all the punishment due to them up to the time they gain the indulgence. And for the rest of their lives, whenever they go to confession the priest will have the power to grant them a similar indulgence; and they will receive an indulgence again in the very moment when they pass from this life to the next.”

Can you help? Thanks in advance.

Yes, I can help.  The quote appears to be a condensed version of this extract from a Tetzel sermon.  Note the similarities below (placed in bold type). See also my blog entry here.

You may obtain letters of safe conduct from the vicar of our Lord Jesus Christ, by means of which you are able to liberate your soul from the hands of the enemy, and convey it by means of contrition and confession, safe and secure from all pains of Purgatory, into the happy kingdom. For know, that in these letters are stamped and engraven all the merits of Christ's passion there laid bare. Consider, that for each and every mortal sin it is necessary to undergo seven years of penitence after confession and contrition, either in this life or in Purgatory. How many mortal sins are committed in a day, how many in a week, how many in a month, how many in a year, how many in the whole extent of life! They are well-nigh numberless, and those that commit them must needs suffer endless punishment in the burning pains of Purgatory. But with these confessional letters you will be able at any time in life to obtain full indulgence for all penalties imposed upon you, in all cases except the four reserved to the Apostolic See. Thence throughout your whole life, whenever you wish to make confession, you may receive the same remission, except in cases reserved to the Pope, and afterwards, at the hour of death, a full indulgence as to all penalties and sins, and your share of all spiritual blessings that exist in the church militant and all its members. Do you not know that when it is necessary for anyone to go to Rome, or undertake any other dangerous journey, he takes his money to a broker and gives a certain per cent—five or six or ten—in order that at Rome or elsewhere he may receive again his funds intact, by means of the letters of this same broker? Are you not willing, then, for the fourth part of a florin, to obtain these letters, by virtue ofwhich you may bring, not your money, but your divine and immortal soul, safe and sound into the land of Paradise?

I'm fairly confident that the quote you sent me is from the very context of this sermon selection. I've worked through many of these sorts of things before. The language of the quote is very similar to that sermon. Keep in mind that there is not a lot of Tetzel available in English, so I would be greatly surprised if the quote you sent me is from something different than the sermon snippet posted above.  

The source of the sermon is cited as, "From the Latin. Gieseler: Ecclesiastical History, Vol. V., pp. 225-26." This source can be found here. There you will find the Latin version of part of Tetzel's sermon. The author also notes, "Tetzel also issued an Instructio summaria for the parochial clergy, in what they were to go to work in behalf of the indulgence..." This is probably the "letter" you're referring to.  The source goes back at least one more step to Herr D. Löscher, Reformationsacten, whom I think, published in the 18th century. I do not have access to that. It may be online somewhere, I don't know.