The story
From Lewis Carroll's Through the Looking-Glass (1871), where Alice is offered “jam to-morrow and jam yesterday — but never jam to-day”. This is a pun on a mnemonic for the usage of jam, iam in Latin (note i/j conflation in Latin spelling), which means “now”, but only in the future or past tense, not in the present (which is instead nunc).
Etymology from Wiktionary, CC BY-SA 4.0.