I am well aware of the Toil and Blood and Treasure, that it will cost Us to maintain this Declaration, and support and defend these States. — Yet through all the Gloom I can see the Rays of ravishing Light and Glory. I can see that the End is more than worth all the Means. And that Posterity will tryumph in that Days Transaction, even altho We should rue it, which I trust in God We shall not.

John Adams (1735-1826) American lawyer, Founding Father, statesman, US President (1797-1801)

Letter (1776-07-03, p.m.) to Abigail Adams
    (Source)

In the original draft, the ending lines read: "And that Posterity will tryumph altho you and I may rue it which I trust in God We shall not."

Early printings of this letter (and that of the morning) changed the recipient to an unnamed male friend. They were used by some (given the date on them and references elsewhere in them) to argue that Independence Day should be celebrated on July 2nd; others published versions with the dates modified to align with a July 4th date for the holiday. The record was not clarified until Charles Francis Adams (grandson of John and Abigail) published a record of his grandparents' correspondence in 1876.

For the record, Independence was voted on and approved by the Continental Congress on 1776-07-02, and the final text of the Declaration of Independence approved and signed on 1776-07-04. Adams was writing on the day in-between.