“We fret ourselves to reform life, in order that posterity may be happy, and posterity will say as usual: "In the past it used to be better, the present is worse than the past."”

Ill Fares the Land (2010), Ch. 2 : The World We Have Lost

In a debate in the Irish House of Commons on the vote of a grant which was recommended by Sir John Parnell, Chancellor of the Exchequer, as one not likely to be felt burdensome for many years to come, it was observed in reply that the House had no right to load posterity with a debt for what could in no degree operate to their advantage. This quotation was Sir Boyle's response.
[Barrington, Jonah, Personal sketches and recollections of his own times, Chapter XVII https://archive.org/details/personalsketche06barrgoog]

Speech http://hansard.millbanksystems.com/commons/1846/jan/22/address-in-answer-to-the-speech in the House of Commons (22 January 1846).
1840s

Quoted in "Enter Japan" - "Time Magazine" article - July 8, 1940

No. 587 (20 August 1714).
The Spectator (1711–1714)

2013, Second Inaugural Address (January 2013)
Context: We, the people, still believe that our obligations as Americans are not just to ourselves, but to all posterity.  We will respond to the threat of climate change, knowing that the failure to do so would betray our children and future generations. Some may still deny the overwhelming judgment of science, but none can avoid the devastating impact of raging fires and crippling drought and more powerful storms. The path towards sustainable energy sources will be long and sometimes difficult. But America cannot resist this transition, we must lead it. We cannot cede to other nations the technology that will power new jobs and new industries, we must claim its promise. That’s how we will maintain our economic vitality and our national treasure -- our forests and waterways, our crop lands and snow-capped peaks. That is how we will preserve our planet, commanded to our care by God. That’s what will lend meaning to the creed our fathers once declared.

Variant: Life can be found only in the present moment. The past is gone, the future is not yet here, and if we do not go back to ourselves in the present moment, we cannot be in touch with life.

Source: Barbarian Sentiments - How The American Century Ends (1989), Chapter 1, Dead Stars, p. 3.

The Power of Now (1997)