Within easy reach, though, and without even checking to see if the batteries in the flashlight are still live:
Low-hanging fruit, really: the final page of L’oiseau de feu. Immediately to hand, and it was an obvious place to look. Au pied de la lettre, of course, I haven’t answered the claim! Here the marking is not strictly ritardando (slowing down) but poco a poco allargando (getting broader, little by little). Having played clarinet in the Suite, though, it does not take much further searching to turn up ipsissima verba:
m.354, un poco rit.
To be sure, the authors will feel that sharp practice has been turned upon them: Here I’ve selected a piece still under the influence of Igor Fyodorovich’s great teacher, Nikolai Andreyevich. If the reader allows the authors to funnel him on their garden path, yes, in much of Stravinsky’s later work, these characteristically Romantic fluctuations of tempo are one of the elements quite deliberately pruned away. There is a truth underneath the flip bon mot. And that, too, arguably, is in harmony with the great subject of the book.