Yes, we now have to divide up our time like that, between politics and our equations. But to me our equations are far more important, for politics are only a matter of present concern. A mathematical equation stands forever.

Earliest source located is the book Brighter than a Thousand Suns: A Personal History of the Atomic Scientists by Robert Jungk (1958), p. 249, which says that Einstein made the comment during "a walk with Ernst Straus, a young mathematician acting as his scientific assistant at Princeton."

Earlier, Straus recalled the German version of the quote in Helle Zeit, Dunkle Zeit: In Memoriam Albert Einstein (1956) edited by Carl Seelig, p. 71. There the quote was given as Ja, so muß man seine Zeit zwischen der Politik und unseren Gleichungen teilen. Aber unsere Gleichungen sind mir doch viel wichtiger; denn die Politik ist für die Gegenwart da, aber solch eine Gleichung is etwas für die Ewigkeit.

"Equations are more important to me, because politics is for the present, but an equation is something for eternity." From A Briefer History of Time by Stephen Hawking (2005), p. 144.