Laustic ("Nightingale" in Breton) is one of the Lais of Marie de France.
Two knights live next door to each other. One is married and one is not. And, since this was written in the era where the notion of courtly love was really popular, the wife of Knight One is in love with Knight Two, who happily reciprocates. Since this is a courtly love story, everything is very chaste and polite and they limit themselves to the exchange of secret gifts and wistful looks out their windows (which happen to be directly across from one another). And while it is casually mentioned that there is TOTALLY a way to sneak unseen into one another's houses, it's never directly stated that hanky has been pankied.
Eventually, Hubby starts to wonder why his wife has been getting out of bed in the dead of night to go sit by the window and asks her what's up. She, fast thinker that she is, says that she's listening to the nightingale that's singing outside. Because it's perfectly normal for a woman to sneak out of bed in the middle of the night to listen to birds. The husband is probably not fooled, though the poem doesn't say it outright, and he does the only rational thing a man can do in that situation: get all the servants in the house to spend their every waking moment hunting down that damned bird.
They catch it, of course, and he presents it to his wife, saying that it won't keep her awake anymore. The wife asks if she can please keep the nightingale, and Hubby, colossal asshat that he is, kills the bird right then and there out of spite and throws it at her, getting its blood all over her clothes.
She keeps the dead bird and tries to think of a way to tell Loverboy that the relationship is over. She can't exactly send him a note, after all, and as far as he'll know, her silence means she just got tired of him. In the end, she sends him the bird, wrapped up in golden foil, and hopes that it (combined with the rumors of the bird hunt, capture, and subsequent killing that the servants are undoubtedly spreading that very moment) will get the message across. He understands immediately and, since he is the nice guy we are supposed to feel bad for, makes the little bird a little gold coffin with little jewels for its little corpse.
A translation by Judith P. Shoaf is available online in PDF format for anybody with the urge to read the poem.